Added error checking to lua's color_coded require

If the shared object has not been compiled yet, color_coded will not be
able to work, naturally. When lua fails to load the shared object, it
will not output a reasonable error to the user.
Added docs for the new error message
Added api version tracking and error reporting

If color_coded is updated (via vundle or other means), the native API
may need to be recompiled. This is determined by the VimL API and the
native API keeping track of their own versions; if the two versions do
not match, the native API should be recompiled and color_coded will not
work until this happens.