Release Checklist

Verify that all CI tests pass for current master
Tag the release, and push to Github
Wait for tag CI to complete
Download assets from snapshots.mitmproxy.org
Create release notice on Github
Upload wheel to pypi
Update docker-releases repo
Update latest tag on https://hub.docker.com/r/mitmproxy/mitmproxy/~/settings/automated-builds/
Bump the version in https://github.com/mitmproxy/mitmproxy/blob/master/mitmproxy/version.py and update https://github.com/mitmproxy/mitmproxy/blob/master/mitmproxy/io_compat.py in the next commit