Add release notes for RBTools 0.7.3.

Review Request #7313 — Created May 18, 2015 and submitted — Latest diff uploaded

Information

RBTools
release-0.7.x
e2e671d...

Reviewers

This covers all the improvements made to RBTools, including fixes for
Unicode problems, new options, compatibility updates, and more. It also
introduces a compatibility warning for TFS support.

Built the docs and looked through them.

Tested links.