Introduce a new builtin Tarantool module `datetime.lua` for timestamp
and interval types support.

New third_party module - c-dt
-----------------------------

* Integrated chansen/c-dt parser as 3rd party module to the
  Tarantool cmake build process;
* We use tarantool/c-dt instead of original chansen/c-dt to
  have an easier cmake build integration, as we have added some
  changes, which provide cmake support, and allow to rename symbols
  if necessary (this symbol renaming is similar to that we see
  with xxhash or icu).

New built-in module `datetime`
------------------------------

* created a new Tarantool built-in module `datetime`, which uses
  `struct datetime` data structure for keeping timestamp values;
* Lua module uses a number of `dt_*` functions from `c-dt` library,
  but they were renamed to `tnt_dt_*` at the moment of exporting
  from executable - to avoid possible name clashes with external
  libraries.

* At the moment we libc `strftime` for formatting of datetime
  values according to flags passed, i.e. `date:format('%FT%T%z')`
  will return something like '1970-01-01T00:00:00+0000', but
  `date:format('%A %d, %B %Y')` will return 'Thursday 01, January 1970'

* if there is no format provided then we use default
  `tnt_datetime_to_string()` function, which converts datetime
  to their default ISO-8601 output format, i.e.
  `tostring(date)` will return string like "1970-01-01T00:00:00Z"

* There are a number of simplified interfaces
  - totable() for exporting table with attributes names as provided
    by `os.date('*t')`
  - set() method provides unified interface to set values using
    the set of attributes as defined above in totable()

Example,

```
local dt = datetime.new {
	nsec      = 123456789,

	sec       = 19,
	min       = 29,
	hour      = 18,

	day       = 20,
	month     = 8,
	year      = 2021,

	tzoffset  = 180
}

local t = dt:totable()
--[[
{
	sec = 19,
	min = 29,
	wday = 6,
	day = 20,
	nsec = 123456789,
	isdst = false,
	yday = 232,
	tzoffset = 180,
	month = 8,
	year = 2021,
	hour = 18
}
--]]

dt:format()   -- 2021-08-21T14:53:34.032Z
dt:format('%Y-%m-%dT%H:%M:%S')   -- 2021-08-21T14:53:34

dt:set {
	usec      = 123456,

	sec       = 19,
	min       = 29,
	hour      = 18,

	day       = 20,
	month     = 8,
	year      = 2021,

	tzoffset  = 180,

}
dt:set {
	timestamp = 1629476485.124,

	tzoffset  = 180,
}

```

Coverage is

File                 Hits Missed Coverage
-----------------------------------------
builtin/datetime.lua 299  23     92.86%
-----------------------------------------
Total                299  23     92.86%

Part of #5941

@TarantoolBot document
Title: Introduced a new `datetime` module for timestamp and interval support

Create `datetime` module for timestamp and interval types support.
It allows to create date and timestamp values using either object interface,
or via parsing of string values conforming to iso-8601 standard.
One may manipulate (modify, subtract or add) timestamp and interval values.

Please refer to https://hackmd.io/@Mons/S1Vfc_axK#Datetime-in-Tarantool
for a more detailed description of module API.

This patch is the first step for fixing regression introduced in
f998ea39 (digest: introduce FFI bindings for xxHash32/64).
We used xxhash library that is shipped with zstd. However it's
possible that user doesn't use bundled zstd. In such cases we
couldn't export xxhash symbols and build failed with following
error:

```
[ 59%] Linking CXX executable tarantool
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: CMakeFiles/tarantool.dir/exports.c.o:(.data.rel+0xd80): undefined reference to `XXH32'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: CMakeFiles/tarantool.dir/exports.c.o:(.data.rel+0xd88): undefined reference to `XXH32_copyState'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: CMakeFiles/tarantool.dir/exports.c.o:(.data.rel+0xd90): undefined reference to `XXH32_digest'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: CMakeFiles/tarantool.dir/exports.c.o:(.data.rel+0xd98): undefined reference to `XXH32_reset'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: CMakeFiles/tarantool.dir/exports.c.o:(.data.rel+0xda0): undefined reference to `XXH32_update'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: CMakeFiles/tarantool.dir/exports.c.o:(.data.rel+0xda8): undefined reference to `XXH64'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: CMakeFiles/tarantool.dir/exports.c.o:(.data.rel+0xdb0): undefined reference to `XXH64_copyState'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: CMakeFiles/tarantool.dir/exports.c.o:(.data.rel+0xdb8): undefined reference to `XXH64_digest'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: CMakeFiles/tarantool.dir/exports.c.o:(.data.rel+0xdc0): undefined reference to `XXH64_reset'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: CMakeFiles/tarantool.dir/exports.c.o:(.data.rel+0xdc8): undefined reference to `XXH64_update'
collect2: error: ld returned 1 exit status
```

To avoid a problem this patch introduces standalone xxhash library
that will be bundled anyway. It's worth to mention that our
approach is still related to zstd. We use Cyan4973/xxHash that is
used in zstd and passes the same compile flags to it. Single
difference is usage of XXH_NAMESPACE to avoid symbols clashing
with zstd.

Need for #6135

Since the commit ae7e2103 we use internal serializer
thus we no longer need serpent code.

The patch removes the references from the source code
and .gitmodules file, still one might need to run

 | git submodule deinit -f third_party/serpent

manually to clean up the working tree depending
on local git version.

Closes #5517

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

libcurl has a built-in threaded resolver used for asynchronous DNS
requests, however, when DNS server is slow to respond, the request still
hangs tarantool until it is finished. The reason is that curl calls
thread_join on the resolving thread internally upon timeout, making the
calling thread hang until resolution has ended.
Use c-ares as an asynchronous resolver instead to eliminate the problem.

Closes #4591

A manual action is needed after pulling of this commit to actually use
the downstream repository instead of the upstream one:

sed -i -e 's@https://github.com/curl/curl.git@https://github.com/tarantool/curl.git@' .git/config

It is part of our processes to use forked repositories for submodules.

Suggested by Konstantin Osipov.

Hold libcurl-7.65.3. This version is not affected by the following
issues:

* #4180 ('httpc: redirects are broken with libcurl-7.30 and older');
* #4389 ('libcurl memory leak');
* #4397 ('HTTPS seem to be unstable').

After this patch libcurl will be statically linked when
ENABLE_BUNDLED_LIBCURL option is set. This option is set by default.

Closes #4318

@TarantoolBot document
Title: Tarantool dependency list was changed

* Added build dependencies: autoconf, automake, libtool, zlib-devel
  (zlib1g-dev on Debian).
* Added runtime dependencies: zlib (zlib1g on Debian).
* Removed build dependencies: libcurl-devel (libcurl4-openssl-dev on
  Debian).
* Removed runtime dependencies: curl.

The reason is that now we use compiled-in libcurl: so we don't depend on
a system libcurl, but inherit its dependencies.

We will use it for Lua console output format serialization

Part-of #3834

Made tarantoolctl compatible with luarocks-3.x.

Fixes #4052.

Add fixed-point decimal type to tarantool core.
Adapt decNumber floating-point decimal library for the purpose, write a
small wrapper and add unit tests.

A new decimal type is an alias for decNumber numbers from the decNumber
library.
Arithmetic operations (+, -, *, /) and some mathematic functions
(ln, log10, exp, pow, sqrt) are available together with methods to
pack and unpack decimal to and from its packed representation (useful
for serialization).

We introduce a single context for all the arithmetic operations
on decimals, which enforces both number precision and scale to be
in range [0, 38]. NaNs and Infinities are restricted.

Part of #692

Usage:

    tarantoolctl rocks install ROCK - install a rock
    tarantoolctl rocks remove ROCK - remove a rock
    tarantoolctl rocks show ROCK - show information about an installed rock
    tarantoolctl rocks search PATTERN - search repository for rocks
    tarantoolctl rocks list - list all installed rocks

There are no other commands, options, configuration files. Our official
repository (http://rocks.tarantool.org) works out of the box. All rocks
are installed to ${PWD}/.rocks directory to support separate rocks trees
per project, as proposed by #2067. Rockspec can use "tarantool >= 1.7.x"
inside dependencies = {} block to depend on a specific Tarantool version.

LuaRocks has been slightly hacked to support custom configuration
via site_config.lua. There are no other changes in the upstream code.
It is not a fork and it isn't going to be a fork. All formats, layouts
and rockspecs are 100% compatible with the upstream LuaRocks 2017-07-10.

This feature intentionally doesn't have CMake option to disable it,
because it should be provided on all available platforms out of the box.

Other changes:

 * Add ${PWD}/.rocks to default package.path/package.cpath
 * Hack tarantoolctl to display subcommands in --help.
   Currently command line arguments handling are not perfect, but
   it can be fixed only by a new argparse implementation.

Closes #2067

Sophia was an experimental storage engine in 1.6.x.
Please use 'vinyl' engine in Tarantool 1.7 instead.

Closes #2040

Needed for #1689

* Use our own fork
* Fix typo in CMakeLists.txt
* Update build dependecies in README.md
* Fix a potential bug with buffer size calculation in ss_lz4filter_next()

Bump memory limit to 2GB

Requested by @kostja

move tarantool/sophia to tarantool-1.6 branch

Support multi-part keys. Allow key duplicate
compaction. Reduce storage cost, encode metadata,
do not store msgpack (except value part).
Reconstruct tuple on read using index schema.

[replication]

JOIN support temporary put to not working
condition: there is no way to access possibly
deleted space schema during the operation
for a tuple reconstruction
(multi-thread).

recreate space key_def during join; enable join

sophia: make every operation asynchronous

sophia: fix join cursor and tests

sophia: implement delayed update operation

sophia: make delete write-only

implement Handler::executeReplace

sophia: merge fixes

make upsert operation an engine specific

sophia: make update logic common to memtx

sophia-integration: switch to Sophia v1.2.3; implement upsert

sophia: add half_commit mode support

This mode disables conflict resolution for
'prepared' transactions and solves the issue with
concurrent write-write conflicts during wal write/yield.

sophia: do not allocate tuple during replace or update; refactoring

sophia: extend and reorganize test suite

sophia: implement box.sophia()

sophia: #681: support or produce error on space::alter

sophia: extend recover tests

sophia: add separate iterator tests

box: enable per-engine select

    * add executeSelect() into engine handler API
    * add MemtxIndex; move preallocated m_position from Index to MemtxIndex
    * remove it->close()
    * remove IteratorGuard class

    note: Sysview and Sophia engines yet share the same select code in
    engine::executeSelect() (which does iterator alloc-free)

box: remove close call from box_iterator_free()

Major changes:

 - All common logic and code from all serializes replaced by
   luaL_field/luaL_serializer functions
 - All features and methods were unified
 - cdata support added to JSON
 - ffi's .NULL added to JSON
 - .cfg{} method added to MsgPack, YAML and JSON
 - .new() method added to MsgPack and YAML
 - NaN and Inf checks ported from JSON
 - array vs map detection logic ported from JSON
 - support for __serialize hint added for table/cdata/userdata
 - _serializer_compact and _serializer_type superseded by __serialize
 - 64-bit integers encoding/decoding fixed in JSON and YAML
 - floating point encoding/decoding fixed in YAML
 - JSON was converted from submodule
 - New TAP-based tests added for MsgPack, MsgPackFFI, YAML, JSON