[announcement] Release Candidate 3.9.0.0-rc2

[Marcus Müller]

Dear SDR community in the best beam from that one could wish for,

It's time. We're doing a GNU Radio Release, 3.9, as promised (but way
later than promised, sorry).

Currently, you'll already find a maint-3.9 branch available for your
enjoyment, and there's an RC2 on it.

The release is planned for next week.

As I'm still in the process of gathering all the changes into a
human-readable CHANGELOG, I can't give you a full rundown of changes and
features in this email, but I know that quite a bit of all this has been
expected, and even controversially discussed:

- Python 3 only
- C++ standard bumped to C++14
- Replacing of SWIG by Pybind11

Of course, there's much, much more going on here. We've got critical
improvements in PMT, we've got new Qt blocks, better code
organization/maintainability, bug fixes by the pound, …

All in all, the changes demanded from a GNU Radio 3.8 user are none to
few; from an OOT developer, we offer better CMake support, and if your
OOT contains C++ code, then you'll have to use Pybind11 to wrap it now,
your SWIG files, they do nothing. Luckily, 3.9's gr_modtool has
automatisms for you.

Obviously, 3.8 isn't being dropped, now that it's taken up a solid user
base. We need to put in place a couple of mechanisms and guides on how
to contribute, and we'll need to figure out a strategy to get bugfixes
backported with the least amount of effort possible.

Best regards,
Marcus