Prepare for the Review Bot 3.0 release.
Review Request #11484 — Created Feb. 24, 2021 and submitted — Latest diff uploaded
This adds release notes for the changes in 3.0, and gets packaging ready
for Python 2/3 builds. Classifiers have also been updated to reflect the
versions of Python and Review Board these are compatible with.
Built the docs. Tested that all links/references were correct.
Built test wheels for the release.