Introduce HasCallStack on new GHC versions

[MaximilianAlgehed]

Closes #235

[nick8325]

I suppose we could avoid duplicating the type signatures by doing something like:

#ifndef NO_CALLSTACK
import GHC.Stack
#define WITHCALLSTACK(ty) HasCallStack => ty
#else
#define WITHCALLSTACK(ty) ty
#endif

and then the type signatures would just be e.g. resize :: WITHCALLSTACK(Int -> Gen a -> Gen a).

[MaximilianAlgehed]

That's a good idea. I was thinking about doing something like type WithCallStack a = a or similar but I wasn't confident that no compiler would complain about that (though they shouldn't?!)

[MaximilianAlgehed]

But the macro idea is nicer because it won't show up in the Haddocks.