Add release notes for Djblets 0.8.28.

Review Request #8613 — Created Jan. 11, 2017 and submitted — Latest diff uploaded

Information

Djblets
release-0.8.x
58bb2fa...

Reviewers

This covers the updates to the development mode packaging for Djblets,
the introduction of the new @cached_property decorator, log filtering,
and some bug fixes.

Checked for spelling errors.

Built the docs.