docs: document new GLOB_MARK constants.
docs: document new GLOB_MARK constants.

* ext/posix/glob.c (Constants): Add an LDoc Constants section for
the new GLOB_MARK constant exported from posix.glob.

Signed-off-by: Gary V. Vaughan <f9023000f29773649f3850298becb9544b5fd6a9@gnu.org>

luaposix/luaposix