Make type families in Data.Row.Internal polykinded

[jqyu]

#19

The primary motivation is to be able to use .== and .+ to construct rows of kinds other than *. Examples.lhs compiles without any changes, however this change is potentially breaking because Forall is now poly-kinded and thus previously working programs may require additional annotations to compile.

The changes to the Forall class seem to be the sole reason why Data.Row.Record and Data.Row.Variants needed to be touched. At a high level it makes sense to me to make said class poly-kinded since we could have something like newtype RecF (r :: Row (* -> *)) (a :: *), newtype VarF (r :: Row (* -> *)) (a :: *) for which we would be able to write instances Forall f Functor => Functor (RecF r), Forall f Functor => Functor (VarF r).

I don't totally understand the type signatures though, so if I messed up anywhere it's probably there.

[strake]

LGTM, @dwincort what say you?

[dwincort]

Thanks for putting in the work!