Improve serializers:

* Many nested levels of associations can now insert
  their information alongside the original when
  embed :ids, :include => true is true
* Add support for passing options to serializers
* Fix Array serializers so they don't try to insert
  roots for each child object and so they can be
  provided a root.
* TODO: Array serializers should require a root
* TODO: Make merging associations at the root more
  efficient if possible

lib/action_controller/serialization.rb

@@ -38,7 +38,7 @@ module ActionController
 
     def _render_option_json(json, options)
       if json.respond_to?(:active_model_serializer) && (serializer = json.active_model_serializer)
-        json = serializer.new(json, serialization_scope)
+        json = serializer.new(json, serialization_scope, options)
       end
       super
     end