maint: use gnulib's maint.mk and support scripts release procedure.

maint: use gnulib's maint.mk and support scripts release procedure.

* Makefile.maint: Removed.
* configure.ac (LASTRELEASE, lt_major, lt_minor, lt_micro, lt_alpha):
All removed. Makefile.maint was the only client.
* HACKING (Release Procedure): Removed.
* bootstrap.conf (gnulib_modules): Add announce-gen,
do-release-commit-and-tag, gendocs, gnu-web-doc-update, gnupload and
readme-release.
* cfg.mk (manual_title): Set it for web-manual rule.
(announcement_Cc_): Release announcement email addresses.
* Makefile.am (build_scripts): Add to EXTRA_DIST additional files
imported from gnulib for maint.mk release procedure.
* NEWS: Updated.

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