Add URL to serializers (closes #61)

Thanks so much to @vanstee for the initial
implementation!

lib/action_controller/serialization.rb

@@ -49,6 +49,7 @@ module ActionController
 
       if serializer
         options[:scope] = serialization_scope
+        options[:url_options] = url_options
         json = serializer.new(json, options.merge(default_serializer_options || {}))
       end
       super