refactor: move DEPRECATED, export et.al. from `base` to `debug`.

* specs/base_spec.yaml (export, DEPRECATED): Move from here...
* specs/debug_spec.yaml (export, DEPRECATED): ...to here.
* specs/base_spec.yaml: Remove unused file.
* specs/specs.mk (specl_SPECS): Remove specs/base_spec.yaml.
* lib/std/base.lua (DEPRECATED, DEPRECATIONMSG, argcheck)
(argerror, arglen, argscheck, export, getcompat, setcompat)
(toomanyarg_fmt): Move from here...
* lib/std/debug.lua (DEPRECATED, DEPRECATIONMSG, argcheck)
(argerror, arglen, argscheck, export, getcompat, setcompat)
(toomanyarg_fmt): ...to here.  Adjust all callers.
* lib/std/base.lua (argpairs, checktype, concat, formaterror)
(getfenv, getinfo, match, merge, normalize, permutations)
(setfenv, whatpath): Move from here...
* lib/std/debug.lua (argpairs, checktype, concat, formaterror)
(getfenv, getinfo, match, merge, normalize, permutations)
(setfenv, whatpath): ...to here, but elide their definitions
if _DEBUG.argcheck is false, or equivalent.
* NEWS: Update.

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