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

lib/active_model/serializer.rb

@@ -380,6 +380,10 @@ module ActiveModel
       @object, @options = object, options
     end
 
+    def url_options
+      @options[:url_options]
+    end
+
     # Returns a json representation of the serializable
     # object including the root.
     def as_json(options=nil)

lib/active_model_serializers.rb

@@ -10,6 +10,12 @@ if defined?(Rails)
         Rails::Generators.configure!(app.config.generators)
         require "generators/resource_override"
       end
+
+      initializer "include_routes.active_model_serializer" do |app|
+        ActiveSupport.on_load(:active_model_serializers) do
+          include app.routes.url_helpers
+        end
+      end
     end
   end
 end