Fix capitalization

[tvquizphd]

This contains fixes previously bundled in PR #39.
This adds new tests (that currently fail on main), and it breaks some existing tests.
Before we could merge this PR, we would need to merge PR #39 and PR #44.

I've found a few miscellaneous capitalization issues with main that I thought I'd address. I'm operating under a few assumptions I've made by observing the general behavior of nspell/main:

• UPPERCASE INPUT should always produce UPPERCASE OUTPUT
• Sentence Case Input should produce Sentence Case Output
  • unless the output is in the dictionary as UPPERCASE
• lowercase input should output lowercase
  • unless the output is in the dictionary as Sentence Case or UPPERCASE
• FuNkY caSE should output FuNkY caSE
  • unless the output is in the dictionary as Sentence Case or UPPERCASE