configury: make posix module version dynamic.

* lib/posix.lua: Move from here...
* lib/posix.lua.in: ...to here.
(version): Use @PACKAGE_STRING@ in place of hard-coded 33.
* configure.ac (AC_CONFIG_FILES): Add lib/posix.lua.
* .gitignore: Add lib/posix.lua.

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