consider using black formatter

[achiang]

Many upstream projects are converging to black, and we did so at my former employer as well. It's extremely opinionated (and I found it somewhat ugly at first sight), but on the other hand, it:

• completely eliminated all discussions around style internally
• is nice to read open source code that uses it too, so that hopping from codebase to codebase is less jarring

Consider using it in this project too?

https://github.com/ambv/black

I'd even go so far as to vote for a single, minor customization of changing the default line length back down to 80 columns (instead of its default of 88), but feel free to ignore that suggestion if it's not your cup of tea.