various fixes

Tried to get this working with python 3 and setuptools.  The results: kinda.  In any case, feel free to use this or not.  Looks like a project with a lot of potential....when it becomes more usable, I hope to come back to it as time permits.

(Also, I'd encourage you to make the rendering backend flexible vs using pydot; there are lots of graph vis packages coming on market...)