Lua: code review. Add rudimentary Lua support.

Implement rudimentary Lua support in the administrative console.
Remove exec module command, it's not used and we now
have Lua for similar purposes.

Add a first Lua module, "box", which
has only one function -- "pack", and test it.
'pack' is derived from box.tbuf module in the
original Lua patch.

Fix a bug in box-protocol.txt, tuple format
description.

Add a copyright header to include/errcode.h (unrelated).

Implement a prototype for Lua initialization
procedure: there is a function tarantool_lua_init(),
which any code, core or modules, can call.
tarantool_lua_init() calls mod_lua_init() to
add module-specific Lua extentions.

Fix a bug in mod/CMakeLists.txt, generate_admin_c
CMake target didn't exist, so admin.m wasn't
re-generated correctly when admin.rl was changed.