Fields and Methods no longer stash the class type; just the ClassData object.
class_lookup, load_class, get_loaded_class all take a string for the classname rather than a type object. This massively reduces the places in which we use types.

I still have to remove types from a few places where they are used to convert between internal/external representations without a ClassData object.

Another milestone toward #116.
Merge branch 'master' of https://github.com/int3/doppio

Conflicts:
	src/ClassData.coffee
	src/exceptions.coffee