Grape formatter feature requested in rails-api#1268

 - adds handling for when the returned resource is not serializable via ams
 - fix for when resource is an Array
 - Moves grape include to grape namespace. Changes Enumerable to Array because a plain hash is enumerable.
 - Add integration test
 - Refine scope of Grape version dependency
 - Assert that the response is equal to a manually defined JSON string
 - Add single module to include in Grape projects
 - Create a Serializable Resource to test rails-api from Grape
 - Update docs
 - Fix discrepency between ActiveRecord 4.0 - 4.1 and 4.2
 - Updated Changelog

active_model_serializers.gemspec

@@ -54,4 +54,5 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'timecop', '~> 0.7'
   spec.add_development_dependency 'grape', '~> 0.13'
   spec.add_development_dependency 'minitest-reporters'
+  spec.add_development_dependency 'grape', '~> 0.13'
 end