shallow_array_clone (internal function) is a lot simpler now
adding toJSONAsync to Collection, Model and Relationalmodel. allows an object to be serialized such that its sub-parts (ie models in a collection, or relations in a relational model) are done one at a time, not all at once. in cases where it takes a large amount of CPU to serialize an object, this can give the browser breathing room (and be the difference between a smooth serialization that takes longer, or a blocked browser interface)