Add release notes for Djblets 0.10 beta 1.

Review Request #8848 — Created March 26, 2017 and submitted — Latest diff uploaded

Information

Djblets
release-0.10.x
08e4c32...

Reviewers

This covers all the new features going into 0.10 beta 1, including
integrations, conditions, avatars, feature checks, registries, form
improvements, and much more.

The documentation also references the upcoming 0.9.7 release, which is
not out yet but should be by the time we release 0.10 beta 1.

There are also fixes for reference linking, both in the Djblets guides
and the code base documentation.

Built the release notes and read through them.

Checked for spelling errors and doc build warnings.