lib: Add Lua API for argument checking.

* lib/zile/lib.lua (argerror): New function. Equivalent to
luaL_argerror.
(typeerror): New function. Higher level call that builds a type
mismatch error message and calls argerror.
(argcheck): New function. Equivalent to luaL_argcheck. This is
where the heavy lifting happens, and mismatches between expected
and actual argument types are found and diagnosed.
(iscallable, recase, stack): Add LDocs.
* build-aux/config.ld.in (file): Add lib.lua.
* local.mk (dist_modules_DATA): Add generated zile.lib.html.

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