Adding Fragment Cache to AMS

It's an upgrade based on the new Cache implementation #693.
It allows to use the Rails conventions to cache
specific attributes or associations.
It's based on the Cache Composition implementation.

test/adapter/json/has_many_test.rb

@@ -6,6 +6,7 @@ module ActiveModel
       class Json
         class HasManyTestTest < Minitest::Test
           def setup
+            ActionController::Base.cache_store.clear
             @author = Author.new(id: 1, name: 'Steve K.')
             @post = Post.new(title: 'New Post', body: 'Body')
             @first_comment = Comment.new(id: 1, body: 'ZOMG A COMMENT')