Push new release branch:
1. make sure branches 'main' and 'release' are synced up locally, check out main
2. update kDemumbleVersion in demumble.cc with new version (with ".git"), then
       git commit -am 'mark this 1.0.0.git'
3. git checkout release; git merge main
4. fix version number in src/version.cc (it will conflict in the above)
5. commit, tag, push (don't forget to push --tags), build binaries
       # on the 'release' branch
       git commit -am v1.0.0; git push origin release
       git tag v1.0.0; git push --tags
       ./dist.py
       # Push the 1.0.0.git change on main too:
       git checkout main; git push origin main
6. add demumble-{linux,mac,win}.zip to https://github.com/nico/demumble/releases
