-Added CustomCreationConverter
-Added IsReference to JsonContainerAttribute
-Added PreserveReferencesHandling to JsonSerializer
-Added IReferenceResolver to JsonSerializer
-Split internals of JsonSerializer into JsonSerializerWriter (serializes) and JsonSerializerReader (deserializes)
-Moved serialize stack from JsonWriter (yuck) to JsonSerializerWriter (yay)
-Added FromObject overload with JsonSerializer argument for cases when state is needed