Automate changelist contents

[derekbruening]

With #2861 we finally have our CI buliding our official release packages. This is a feature request to switch to automated changelist construction, populating both the Github Release description and the html docs.

The simplest method would be to take the list of commits and use their titles or some tags inside them to extract the features. Or, if we move to more-frequent releases, perhaps listing all commits since the last release.