Simplified serialization (and hopefully made it more powerful) by making to_primitive on MultiType receive a model_converter. This fixes bugs regarding roles and serializable fields in deeply embedded object hierarchies
Refactored serialization heavily by making the compound types alittle cleverer. Added serialization to the MultiType which is to_primitive + filter by role. I think this results in cleaner and more extendible code. flatten can also be refactored, even without touching the compound types.