Working python3 version

[perkinslr]

This is my ancient port (from about 2016) to python3.5+. It needs some work to reconcile the changes upstream (and to clean up some of the dirty hacks I did to get it functional), but at least some parts of it should help other efforts to get this to python3 (and it may be a better starting point than the last 2.7 release).

Note that it does not use six, as I had no need to run on python2 after the migration. Instead, I used 2to3 (from python3.4), which broke things terribly, and then spent far too much time sorting out what that stupid script broke.