Add black configuration consistent with other tools?

[Rocco Meli]

pyproject.toml:

[tool.black]
line-length = 80
extend-exclude = "versioneer.py"

[Lily Wang]

Sounds good. 80 not 79? Is that one of the black defaults?

[Rocco Meli]

Black's default is 88 (see https://black.readthedocs.io/en/stable/the_black_code_style/current_style.html#line-length for more info).

I'm suggesting 80 because it is the setting used for other tools in setup.cfg.