Update the 0.9 release notes to be comprehensive.

Review Request #7737 — Created Oct. 25, 2015 and submitted — Latest diff uploaded

Information

Djblets
release-0.9.x

Reviewers

This updates the 0.9 release notes to contain the entire list of changes
made since the 0.8 series, and to contain further compatibility and
installation notes.

Built the docs and went through them, checking all links and content.