This is pure refactoring. No functional changes intended.

Closes #1811

Convert requeset.cc to request.c (plain C) to make
request_normalize_ops() callable from C. Move all prepareatory
work from Vinyl_Space::executeUpsert() to vy_upsert() to make
vy_upsert() callable from other contexts.

Encapsulate vy_insert() in vy_replace(), to make vy_replace()
a single entry point to all kinds of replaces. This is necessary
to make vy_replace() easily usable in other contexts.

Remove VinylEngine::recovery_complete, which was fully
dependent on vy_env::status. Provide public access to
vy_env::status.

In preparation for folding of memtx_replace_build_next() in scope
of recovery refactoring, mvoe all replace functions to memtx_space.cc

No semantical changes.

Don't count snapshot rows when recovering bootstrap.snap.
Add a comment to memtx_add_primary_key()

In case of multi-level compaction, we compact and hence delete not all
runs, so we must not delete the runs left on the list from the metadata
log, but we do now. This breaks recovery. Fix this.

Add error injection for vinyl schedule timeout. Used for vinyl
error injection tests.

New test for vinyl checkpoint

Before dumping or compacting a range, consider coalescing it with its
neighbors. Only coalesce two adjacent ranges if the total size of disk
space and in-memory data occupied by them is <= range_size / 2, to avoid
split-coalesce oscillations.

Closes #1735

Rename tuple.cc, tuple_convert.cc, tuple_format.cc

No semantic changes.

* Re-order code in tuple.h, tuple_format.h and key_def.h
* Add _xc prefixes to tuple.h functions
* Fix an unchecked exception in box_tuple_iterator()

Closes #2038

Add helpers to decode numbers and use them throughout the code.

tuple_update/upsert was inlined in memtx_space and
box_tuple_update/upsert.

Fixes #1778

Needed to ensure that update_optimize will work
after implementation of common memory level
for txv and vy_mems.

Needed for #1908

Exactly the same piece of code (including comment) used by both dump and
compact. Factor it out into a separate function.

All the three functions that need a write iterator, dump, compact, and
split, reuse the same code for initialization of the write iterator.
Factor it out into a separate function.

* Use SNPRINT() macro from util.h
* Prettify formatting with missing schema (e.g. "user@localhost")
* Add Lua test case

Fixes #1924

1024MB is a lot for small devices and virtual machines.
256 MB is more than sufficient to play with a database,
and will make life easier when trying the database for
the first time.

Closes #1692

Change order of traversal in merge iterator to direct,
getting ready for avoiding reading from disk in case of cache hit

Required to check if a range should be coalesced with its neighbors.

 - Do not unaccount mem from the index and unlink it from the scheduler
   in vy_range_delete(), because it violates encapsulation. Let's just
   delete it there and leave accounting to specialized helpers, as we do
   in case of runs.
 - Delete vy_range_delete_mem() helper, because it has nothing to do
   with range - it unaccounts a mem from the *index* and removes it from
   the *scheduler*, and then frees it.
 - Make vy_index_{acct,unacct}_range() helpers handle mems as well, as
   those are a part of each range.
 - Drop vy_index_acct_range_dumped() helper. Use unacct/acct pair
   instead.

Hopefully, ths patch makes the code easier to follow.

Besides vy_run_total(), which returns the size of run data file on disk,
there's also vy_run_size() which returns the size of run and page info
structs in memory. The latter doesn't make much sense, so let's drop it
and rename vy_run_total() to vy_run_size().

 - Generate random keys to prevent compression.
 - Expect 2 ranges, not 4, because we do not split a range unless
   it was compacted. We could make the test generate 4 ranges by
   issuing snapshot more often, but that would increase execution
   time, so leave it as is.

Follow up a49673c9

* update the default level_size_ratio
* rename level_size_ratio to run_size_ratio
* rename max_runs_per_level to run_count_per_level

To follow the LSM tree design, group runs of the same range into levels.
The division is ephemeral, it is recomputed after each dump and not
stored in vy_range struct. The size of the first level is set to the
largest run dumped since the last compaction. The size of each
subsequent level is level_size_ratio times larger than previous one.
When the number of runs at a level exceeds max_runs_per_level, all runs
of the maximal level that exceeds the limitation as well as all runs and
mems of preceding levels are compacted. max_runs_per_level and
level_size_ratio are set in index config. By default, they equal to 2
and 10, respectively.

Closes #1821

Fix naming convention.

Follow up the previous patch.