lexer:
- Un-stringify errors
- Reserve more words
- Doc the comments
parser:
- MASSIVE changes to peek, peek_if, next_if, consume_if=>expect.
- Keep track of when EOF is allowable
- TKind is stupidly cheap with >100 niches, so we can fit like 4 of them in a single ParseError lmao
- TODO: make sure EOF/UnexpectedEOF propagation is correct. It seems... Kinda Not correct.
- Add meta-expressions
