Integrate fontsets with Haskell Stylist.

Implement Stylist traits for FontConfig patterns!

Improve memory safety & error checks.

Expose font weight adjustments & correct current-config refcount.

Finish initial redraft

Write init/finalize & pattern language bindings, haskell-side!

Encode & decode charsets on C side (fix Haskell side)

Datamodel FontConfig in Haskell.