Prototypes with typeclasses

This branch has a few additional random optimisations than specifically prototypes for datatypes and typeclasses, but here it is anyway.

- Prototypes for data types
- Prototypes for typeclasses
- No empty `__superclasses` anymore
- Typeclass objects now have the superclasses as direct properties rather than stored inside a `__superclasses` object
- Applications like `f({})` to force thunks are now inlined to just be regular javascript `f()` calls.
Adding a `C.__unused` makes sense to me.

We could just take it out entirely alternatively, as it makes no difference to execution, it's just for when reading the generated JS.