Remove "optimized" autocommit code when working with a single index,
tarantool always creates a transaction in engine even for
autocommit mode. This optimization, in other words, could
(potentially) save only a little bit of CPU in case of
autocommit and only-primary-key space.

* remove trigger (not used)

* remove the built-in write ahead log (never used in Tarantool)

We need an online backup for all engines. The current
backup in phia only works when its own write ahead log is enabled,
which is never the case with tarantool.
@todo: add rsync-friendly backup to phia, just like
is already the case for memtx.

* remove ss_cond, ss_mutex, use Tarantool primitives instead.
* refactoring of tt_pthread.h to avoid using single-letter
variables

* remove object pools
* small refactoring of "long" tests.

Move long_run suite to engine_long. phia tests crash (wrong results).

Tweak php example in the doc book

* renames
* begin removing the object runtime madness

* rename sp_* -> phia_*

* remove sp_prepare(), unused, undocumented, unimplemented
* remove sp_error()
* remove sp_poll()

* remove PHIA_BUILD
* remove GNU_SOURCE

Use config.h instead.

Finish removal of third-party code from phia.c.

Prepare to convert zstd to a submodule.

Thanks for clang 3.6

* 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()