Spellcheck the repo

[sjspielman]

Closes #164

Spellchecking the repo! Filing as a draft to first catch and fix the spelling errors.

[sjspielman]

This is now ready for review. As part of review, please weigh in on:

• Do we want to keep the GHA checking all these files? (maybe we can remove the files argument altogether at this point?)
• If we do not want to do ^, I could also remove the partial words from the dictionary, e.g. ual derived from manual.

[jashapiro]

LGTM. I'd probably just check all files to keep things simpler. I suggested another way to exclude files from checks if we want to do that.

Othere than that, just a few minor comments.

[jashapiro]

I'd probably just remove this at this point and check everything. I'm not too worried about the partial words added being a problem.

I also thought of another thing we could if we want to exclude particular files: add a step with rm for the files we want the spellchecker to skip.