Add release notes for RBTools 0.7.8.

Review Request #8588 — Created Jan. 3, 2017 and submitted — Latest diff uploaded

Information

RBTools
release-0.7.x
b63fc55...

Reviewers

This covers the work done on the installers for Windows and macOS, as
well as the Unicode fixes and improvements to rbt setup-repo. It's a
smaller release, but an important one from an installer standpoint.

Built the docs and read through them.

Checked for spelling errors.