Proposal: use black, typing, PEP 8

[technillogue]

PEP 8

Function names should be lowercase, with words separated by underscores as necessary to improve readability. Variable names follow the same convention as function names. mixedCase is allowed only in contexts where that's already the prevailing style (e.g. threading.py), to retain backwards compatibility.

This is the stuff I already partially have, would prefer for my fork/usage of splitwise, am happy to do but would otherwise keep in my fork, but maybe these would be welcome upstream?

[namaggarwal]

The problem with this is that it would be breaking changes. We can maintain function aliases and I would welcome that.