use black formatting

[bhazelton]

We've gone to this in pyuvdata and pyradiosky so it makes sense to do it here. It does make a lot of changes, so should be done when there is a break in branches/PRs.

[steven-murray]

For anyone who reads this: if you're working on a PR, it would be prudent to try to ensure that you're writing in black style -- this will make the transition easier when it does come. You can blacken a file by running black <filename>. I don't know if you can do parts of files though.

[mkolopanis]

a relevant issue to your inquiry. psf/black#511