Add release notes for Review Board 2.0.15.

Review Request #7070 — Created March 16, 2015 and submitted — Latest diff uploaded

Information

Review Board
release-2.0.x
6d2ac9a...

Reviewers

This covers all the new search features, plus the bug fixes for negative
counters in the dashboard, Enable Markdown checkbox, the display of the
internal review request status field, and more.

Built and viewed the docs. Looked correct, and no errors.