Parsing with attoparsec

[JustusAdam]

There is an experimental branch which uses attoparsec instead of parsec.

It type checks but does not succeed the tests yet.

It'd be nice to fix it and then compare it to the parsec parser.

[mrkkrp]

Take a look at Megaparsec too: https://hackage.haskell.org/package/megaparsec. Switching from Parsec to Megaparsec is almost mechanic. Here is the site: https://mrkkrp.github.io/megaparsec/.