Incorporate recff_cdata_arith fix.

Fixes #1617

Use just a few more letters in variable names.

Remove the notion of error flags (properties), it was removed
from the client-server protocol and not used in any client.

* Merge vy_branch_update_stat() into vy_branch_write()
* Refactor firstvalue/lastvalue logic in vy_branch_write()
* memcpy() entire tuple instead of copying field by field
* Remove sf_comparable_size() and sf_comparable_write()
* Add missing vy_buf_free(&compressed)

Needed for #1594.

* finish the renames in code and comments, spotted by PeterG
* use configuration parameters from key_def, without an
  unnecessary key_def

* remove sitx

The server could crash at exit because cord_destroy() would
attempt to access thread-local memory of the cord being destroyed,
after the undelrying thread ceased to exist.

Move fiber pool to fiber.c, store in struct cord, and
destroy properly in cord_destroy().

*)Removed virtual version of buffer iterator
*)Placed a temporary upsert stub in merger
*)Added VINYL_EQ order to in-memory tree iterator

Length of MessagePack field is always > 0. Use field->size == 0 to
indicate that a partial key doesn't have more parts.

Needed to support NUMBER, SCALAR and other index types.

* merge sx_commit and vinyl_tx_prepare()
* make sure method names follow Tarantool scheme
* remove single-letter variables

* SX -> TX
* sxmanager -> tx_manager
* sxindex -> tx_index

* continue refactoring the information cursor
* move code around so that all vy_info stuff is together

* Fixes #1550 deadlock on ss_quota() during vinyl/stress.test.lua
* Fixes #1584 losing data after snapshot
* Fixes #1600 bad results from engine/recover_snapshot_wal.test.lua
* Fixes useless si_plannerpeek_branch() + si_branch() loops
  caused by false-positive si_plannerpeek_branch() results

This regression was introduced by 1edaeabb

* continue deploying vy_ prefix, use Tarantool naming conventions

* doc: moved to http://github.com/tarantool/doc

Conflicts:
	doc/sphinx/book/user_guide_getting_started.rst
	doc/sphinx/conf.py.in
	third_party/libyaml

Conflicts:
	doc/sphinx/book/app/e_vinyl/index.rst
	doc/sphinx/book/box/atomic.rst
	doc/sphinx/book/box/box_schema.rst
	doc/sphinx/book/box/index.rst
	doc/sphinx/book/box/limitations.rst
	doc/sphinx/book/box/vinyl_diff.rst