WIP ENH: Autopep8

I ran `autopep8` on the codebase. Tests still pass, but I need to go through the files and make sure everything still makes sense, and check for e.g. pyflakes violations. Before I invest time in doing this, I figured I'd check to make sure now is a good time to actually undertake cleaning the code. It doesn't look like there are pending PRs, but I think people have some forks going...?