Example of plotting coordinates on an all-sky map (final pull request)

This should be the final pull request as discussed in issue #2726. There were some problems with my repo, so I had to re-create my branch and so github doesn't allow me to update the original pull request.
Looks like you removed the first example from here?  As I said above, I think that's good, but you'll need to combine this and the previous paragraph, then.