9.10 support

[michaelpj]

Not sure what needs to happen here, but at least updating to use a new ghc-lib-parser.

[jhrcek]

Here's a PR making it compile with 9.10, all tests passing with cabal (check CI in my fork: jhrcek#1). The only thing that seems to be missing is stackage snapshot with 9.10 support so we can upgrade stylish-haskell's stack CI..

[danwdart]

That PR is closed - presumably by code already in upstream - does that mean this ticket can be closed?

[danwdart]

Oops - too fast on the mark there - #480 supplanted it.