thinking through how to handle collections...I think I'm moving in the wrong direction, rather than having collections be a 1st level object on Backone.Siren, they should probably be just stay simple Backbone.Collections and nothing more
fix check for nested sub-entity vs linked sub-entity

the more reliable check seems to be checking for an href property since nested sub-entities use links instead.  Also, a collection might have some properties such as a page offset for example
oops, fix previous commit
Update the collection constructor to auot-generate models
Provide for serialization of Models and Collections

I think Backbone serializes Models and Collections using toJSON before syncing them with the db/server.  By overriding the toJSON method I think it will set us up for automatic easily save to the server.

Rename entities to "resolveEntities" and createa  new "entities" method that simply returns nested entity models