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.

Conflicts:
	.gitmodules
	client/tarantool/tc_print.c
	src/lib/small

pod2man causes too many troubles

* Split libyaml (C library) and lua-yaml (Lua bindings)
* Add support for system libyaml-dev in CMake scripts if
   -DENABLE_BUNDLED_LIBYAML is OFF (default is ON)
* Add libyaml-dev to DEB dependencies

third_party/libyaml/ is completely identical to upstream libyaml 0.1.6.
(libyaml-0-2 in Debian/Ubuntu). Test are passed both with bundled and
system versions of the library.

third_party/lua-yaml/ is patched by me to use luaL_serializer, therefore
upstream version is not suitable for Tarantool.

This patch is needed to pass Debian package checks (lintian).

closes gh-1189

closes gh-1196, closes gh-1159, closes gh-1135, update links in en_US
tutorial.