Add Black functionality and Blacken code

[rybarczykj]

Here's what I did

• Blackened source code (many python files edited)
• Added pyproject.toml file to configure Black formatting, which is be identical to bpython's Black formatting
• Edited setup.md to add instructions for using Black (along with some other details)

Since running Black made a lot of changes to a lot of files, it definitely screws with the blame history a bit. It could be a good idea for me to add a .git-blame-ignore-revs file to implement a recently added git feature which allows people to ignore certain commits when looking at blame history. If you want me to do this before you accept, let me know.

[thomasballinger]

@rybarczykj I've never used this but that sounds great, let's do it. Making the setup.md and big formatting diff changes in separate commits is nice, you might even separate the formatting changes and the config changes too, mostly for my benefit while reviewing but also for future blames.

[thomasballinger]

Closed in favor of #139