Perform versioning within CORD documentation repo

Documentation currently works based on a branch set in git on every repo.

As this won't happen for the 6.0 release, come up with a different method of handling the documentation versioning.

Proposed method from Scott Baker is to do this in the Makefile, creating one branch on that repo, and listing git tags/branches/revisions of other repos in the Makefile. This gets around our current use of `repo` as well.