Create a preliminary NEWS entry for the upcoming v13 release. Lots of
fixes all over the place, but most of them not worth mentioning for the
release. However, we do have some feature improvements as well.
This extends on our model how we do releases. It introduces `NEWS.md`
as the authoritative source of our release-notes. It is pre-populated
with the release-notes from the previous 'v9' release, and contains a
suggestion for the upcoming 'v10'.
Furthermore, this adds `make release` as a simple checklist target that
contains instructions how to create a new release. Note that it is a
passive make-target which has no side-effects at all. It only prints
release information.
With this in place, we can drop `RELEASE.md`, as all information is now
combined in `make release`.
