starting on 1.5.3 release

[John Sichi]

I'm gonna try to wipe off the dust and see if I can get a release out.  There are a couple of new community detection algorithms that are probably close to being mergeable, but the authors have stopped responding to review comments.

After that, I think it's probably time to call the next dev version 1.6, since we should move to Java 21 (or 25?) after the 1.5.3 release goes out.