Implement C stdlib benchmark

[djspiewak]

One of the benchmarks that I think would be particularly interesting is to use the C YACC grammar (the Lex specification is here) to parse the full stdlib. This is the very definition of a real-world test. Critically, the C grammar makes heavy use of LALR(1) features, while simultaneously being entirely unambiguous. I would not want to produce any ASTs (every parser should be Parser[Unit]).

Benchmarking this between parseback, gll-combinators and (ideally!) Scala Parser Combinators would be very instructive.