Implement embedded object typing

Hey @gamache! I'm interested in implementing automatic typing for embedded resources (in particular individual objects within a collection, much as you've done for response-level resources.

The existing approach of examining response headers (i.e., the `type` parameter of the `Content-Type` header) won't necessarily map well to the problem of typing embedded resources. Here I've somewhat arbitrarily chosen to examine the `type` field of each resource. It works for me, but I'd like to hear what you think is the most appropriate default for determining types of embedded resources.

Thanks!