Pandoc Haskell filters

[srid]

Allow users to write a .hs filter (without having to setup the whole Haskell project), and evaluate it using https://github.com/haskell-hint/hint

Aside from Pandoc -> Pandoc we even allow the user to filter Emanote-specific stuff, eg: Note -> Note.

(This is like #263 but using Haskell and Emanote-awareness in filters)