Poor man's atomics based on facilities in stdatomic.h; enables writing
lock-free code in C11 style, see third_party/pmatomic.h for details

* make sure long-run tests pass
* more systematic approach to downcasts to MemtxIndex in
alter/system spaces code

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()

Reason: net.box depends on src/box/lua/tuple.h, src/box/lua/schema.lua,
src/box/lua/call.cc and these dependencies impossible to fix.

box.cfg{} is not required for net.box.

reverts commit 19343e71

* struct stat_counter keeps all statistics data (supports several instances)
* test sends 100 rps, but this methods count only 80
* stat counting bug fixed
* style fixes
* renamed as stat.c to rmean.c

No semantical code chagnes.

* msgpack encoding with lua c api(call, insert, eval, ping)
* remove extra hash lookup in net.box
* review fixes for netbox-write
* rewrite all encoding fucntions using Lua/C
* replace channels with fiber.sleep()/fiber.wakeup()
* review fixes (remove an unnecessary include)

Conflicts:
	src/CMakeLists.txt
	src/ffisyms.cc
	src/lua/init.cc
	test/unit/CMakeLists.txt

This patch adds four new functions to API:

  * luaL_checkuint64()
  * luaL_touint64()
  * luaL_checkint64()
  * luaL_toint64()

This functions are needed to rewrite request encoding in net.box.

The origin was that 'vmdef.lua' was generated in
'${CMAKE_BINARY_DIR}/third_party/luajit/jit/', but was searched in
'${CMAKE_SOURCE_DIR}/...'.
ALSO: when we start to generate *.c files from luajit's libraries we made
statement, that we don't built with OS pre-built luajits.

sio_move_iov is not built to advance both obuf_svp and iov,
tweak the code to make sure it does what's needed.