Updated naming conventions

[Walnut356]

Some terms are modified to disambiguate data type (airborne -> is_airborne, hitlag -> hitlag_remaining)

Some are changed to be more in line with what someone unfamiliar with the API would most likely try to type in when looking for a variable (damage -> percent)

I basically had 3 rules for consistency:

• Defer to slippi/file spec

• Defer to community naming

• If both are wrong/inaccurate/lengthy/inelegant, use best judgement (e.g. "shield" -> file spec "shield size", except that's not the correct term. Shield size is the resulting shield bubble size of the analog value/shield health formula. "Shield health" is the correct term)

I also took the liberty of adding descriptive comments to many of the states in the action states enum, based off of the ssbm datasheet.

All tests pass, hard-coded test strings were updated by hand rather than re-generated-and-replaced to prove that there were no logic changes.

[NickCondron]

I made a PR #56 that will allow you to add doc comments to the constants within pseudo_enum/pseudo_bitmask

[hohav]

The enum-related parts of this PR would no longer belong in peppi but in ssbm-data. The field renames I mostly disagree with, except damage->percent: I still think the latter is a terrible name, but it's used widely enough in the community that I'm willing to accept it in the interests of pragmatism.

More generally, it would be better to open an issue to discuss a sweeping change like this before submitting a PR.