Revised the entire tutorial (file help_en_US.lua):
 * Tested and fixed all sample code snippets.
 * Corrected typos and inconsistent names in screen headers.
 * Updated info about custom delimiters (screen #6).
 * Replaced box.session with fiber (example on screen #10).
 * Swapped screens #11/#12 (fibers/sockets) for smoother story flow.

Removed help-related stub logic (file help.lua).

Updated auto-tests to expect a new output result on help call.

*)updated small submodule
*)test was added

Incompatible changes: server is not removed from box.info.vclock anymore
on delete from _cluster. A new replica re-uses previous server_id and
also last known LSN (was only server_id, but LSN always started from zero).

A prerequisite for #1219 test case.

closes gh-1189

ddl test separated in engine and sophia specific tests
sophia_join.test moved from replication to engine suite

Fix a race condition in status.test

Mhash del function was used incorrectly, resulting in memory access past
the buffer end.

Add a separate error code for the case when a tuple is too large
(larger than slab_alloc_maximal).
The test suite already covered the case.

Test_suite restart disabled
Legacy tests moved to separated suite

added tests

Change the code to use small/rlist.h, to avoid code duplication.
small is self-contained.

Now that we have a very nice title, don't use a custom proc title that
often.