release: use new luarocks 2.2.0 upload command.

* build-aux/release.mk (LUAROCKS): New macro. Default to luarocks.
(upload): New phony rule. Call luarocks upload with release
rockspec file.
(release): Add `$(MAKE) upload`.
* NEWS: Update.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
Release version 7

* NEWS: Record release date.
maint: post-release administrivia.

* NEWS: Add header line for next release.
* .prev-version: Record previous version.
* configure.ac (AC_INIT): Bump version number to 8.
* local.mk (old_NEWS_hash): Auto-update.

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