This reverts commit d72fd069.

Tested and updated building instructions for Mac OS X. (by Elena Shebunyaeva)

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.

https://release.debian.org/migration/testing.pl?package=tarantool:

Trying to update tarantool from 1.6.3.539.g211672f-1 to
1.6.7.551.ga5bafc5-1 (candidate is 25 days old):

+ tarantool/amd64 unsatisfiable Depends: binutils (<< 2.25.90.20151126)
+ missing build on XXX: tarantool-common (from 1.6.3.539.g211672f-1)

This reverts commit 310eb33e.

Conflicts:
	third_party/sophia

Fix #1239 Sophia join does not work

*)updated small submodule
*)test was added

Needed to prepare a fix for #1185
Actually s/_ex_cb/_xc_cb/g.

The official ISO image of Debian GNU/kFreeBSD is broken.
Why we should care about it?

W dep5-copyright-license-name-not-unique (paragraph at line 327)
W missing-license-paragraph-in-dep5-copyright bsd-2-clause (paragraph at line 315)
W spelling-error-in-description develoment development

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).