Remove Rails dependency

Move configuration into a Railtie.
Only dependency is now activemodel

test/generators_test.rb

@@ -1,4 +1,4 @@
-require 'rails'
+require 'test_helper'
 
 class Foo < Rails::Application
 end

test/serialization_test.rb

@@ -39,6 +39,8 @@ class RenderJsonTest < ActionController::TestCase
   end
 
   class TestController < ActionController::Base
+    include ActionController::Serialization
+
     protect_from_forgery
 
     serialization_scope :current_user
@@ -169,4 +171,4 @@ class RenderJsonTest < ActionController::TestCase
     get :render_json_with_serializer_api_but_without_serializer
     assert_match '{"serializable_object":true}', @response.body
   end
-end
+end

test/test_helper.rb

@@ -21,4 +21,4 @@ ActiveSupport::TestCase.class_eval do
   setup do
     @routes = ::TestHelper::Routes
   end
-end
+end