Library could automatically instantiate embedded resources

[butterknight]

Currently, when a resource that contains an embedded resource is fetched, the library won't automatically instantiate the model for the embedded resource (even if the model definition exists) until the relationship descriptor is provided.

This means that fetching a resource with request is problematic if it has an embedded resource that we'd like to instantiate automatically.

I think an embedded resource could be instantiated regardless of relationship descriptors if the model definition for it exists.