Add ability to create multiple resources down a graph with one request

[aultac]

A 99% use case for PUT/POST is to PUT/POST to a location from bookmarks. This means you are assuming that the resources above you in the graph rooted at bookmarks already exist and have the proper media types. We should make this a simple thing to do by enabling you to PUT/POST the top and include keys/types for everything down to the level you want, indicating where resources should go if they need to be made.