Add docstrings everywhere!
Document modules.
Improve handling of invalid FontConfig data.
Fuzz test roundtrip conversions between C & Haskell datastructures!
Properly handle ambiguity in empty char/lang sets.
fuzz-test MessagePack implementations.
Constrain public API.
Encode & decode charsets on C side (fix Haskell side)
Datamodel FontConfig in Haskell.