Create new release

First of course the CHANGELOG should be updated.

Stable release series have an even MINOR number, ongoing development has an uneven MINOR number.

A stable release is generally done with the following steps:

creating an annotated tag with vMAJOR.MINOR.PATCH_stable in git. If it is the first release of a MAJOR.MINOR series, also create the vMAJOR.MINOR branch.
Add the release on https://github.com/paparazzi/paparazzi/releases
As the tarballs that github automatically creates don't include the submodules, run
```
./make_release_tarball.sh
mv paparazzi.tar paparazzi_vMAJOR.MINOR.PATCH_stable.tar
gzip paparazzi_vMAJOR.MINOR.PATCH_stable.tar
```
and upload this tarball to the github release
Update docs if a new stable branch: adjust index.html and add the branch to the pprz-update-dox.sh script on odin.paparazziuav.org

DevGuide/Releasing