Use parser combinators instead of Regex

[pragmatrix]

I'm having a bit of a hard time implementing even simple parsers with Regexes. Therefore I am considering using a parser combinator framework:

Candidates are (ranked by dependents on crates.io):

• 992: nom: Basically unusable syntax-wise, weirdest one, ancient, fast.
• 98: LALRPOP: External files... Nooooo.
• 58: combine: Inspired by Parsec, trait heavy, a bit of trouble passing parsers around. Lots of success stories.
• 20: pom: PEG, so far no downsides. Looks similar to the one I built for F#. slow at construction time
• 5: Chomp: TODO
• 0: Chumsky: Similar to pom. New.

TODO:

• How can we reuse parsers, constructing them may be expensive.

  We can use once_cell, no locking involved if static is already initialized, just one atomic memory read.