Fix warnings

[hdgarrood]

This doesn't fix absolutely every warning; there are still two redundant
import warnings in Text.Parsing.Parser, arising from the imports of
Control.Monad.State.Class and Control.Monad.Trans.

Unfortunately, the compiler (0.7.6.1) is wrong; they are not redundant.
This is now fixed in the compiler, though, so these warnings should just
disappear after upgrading.

[paf31]

Looks good, but why move makeParser etc. out of the where?

[hdgarrood]

Mainly because it was the easiest way to deal with all the shadowed type variables. But I generally prefer using top level declarations where possible, because when you have huge where clauses, any bindings in the where can use arguments bound in the top level declaration, which makes the way data is flowing around in the program a bit harder to follow, I think. There's more to keep in your head at once.

I checked that that module already has an explicit import list, so it won't lead to any new exports.