Add release notes for 2.0.21.
Review Request #7792 — Created Dec. 3, 2015 and submitted — Latest diff uploaded
This covers all the various changes that have gone into this release, including bug fixes for post-commit review, diff caching, GitLab, SSH, and more. It also contains the new Assembla feature, e-mail improvements, and extension improvements.
Built the docs and checked through them. Looked fine.