Lint with black and set up automated black check

[mattwthompson]

Split out from #650. isort and black have some small disagreements that could be resolved here but I would rather deal with those later while resolving some flake8 complaints. The changes here are roughly the minimum to get this adopted as quickly as possible, and I tried to keep the commit history discrete if we wish to roll anything back.

• Tag issue being addressed
• Add tests
• Update docstrings/documentation, if applicable
• Update changelog

[SimonBoothroyd]

I've skimmed over most of the changes and it LGTM and suggested a few minor optional changes. Thanks @mattwthompson !

[mattwthompson]

Thanks @SimonBoothroyd!

[j-wags]

Looks great. Thanks for making the call and merging this in -- I've been hesitating too much on this and it's good to just drop the hammer and deal with the consequences instead of leaving it hanging forever!

[j-wags]

Looks great. Thanks for making the call and merging this in -- I've been hesitating too much on this and it's good to just drop the hammer and deal with the consequences instead of leaving it hanging forever!