Add pre-commit configuration, some new checks and reformat

[Jackenmen]

If you don't want some from the checks that are done here, let me know and I'll remove them.
If you're not okay with doing the reformatting in the same PR that pre-commit configuration is added in, I can also split this PR in two (or in however many pieces you want).

Using pre-commit is as simple as running this in your (preferably global) environment:
pip install -U pre-commit
And then running pre-commit install in the root of your repository.
From now on, pre-commit will automatically run when you make a commit and will let you know if there are issues with any of the checks it runs.