Remove dead code
Add guard
Add ham to stub
as_jsonld only returns contextualized attributes
Recursively contextualize Contextualizable subobjects
Add namespacing support for sub-hashes
Rely on as_json to feed us keys
Fix case where we don't recurse into Mongoid relation

Mongoid relations return proxy objects that fail the idiomatic `case obj ; when ClassName` pattern when testing for mixins (lame). Fix this by actually calling 'is_a?' in lieu of case, which forces Mongoid's hand and loads the referenced doc