Set up basic integration with pre-commit.

[Flameeyes]

This currently only checks for basic file hygiene, namely end-of-file and training whitespace.

This does not yet allow running REUSE, as there's a lot of files without
copyright information that need to be updated.

[tannewt]

Does the whitespace change leave one blank line at the end of the file? I think we tend to.

Looks like some test outputs were changed and broken. They'll need to be exempted.

[Flameeyes]

Does the whitespace change leave one blank line at the end of the file? I think we tend to.

It leaves an empty line the way Emacs and other editors do — which matches what the Adafruit_CircuitPython_* libraries appear to have. It seems to be different in this repo though, and a lot of files have two empty lines, which is what it's correcting.

Looks like some test outputs were changed and broken. They'll need to be exempted.

Yeah I'm still trying to get this all to pass, it's not quite obvious for some of these tests which files need to be ignored. Sorry about that :(

[Flameeyes]

Yay, passed!

I'll follow up with REUSE changes separately, since the CI is a bit heavy, and I don't have as much time as I had a couple of weeks ago, but I do have something working on.

[tannewt]

Ok, great! Thank you!