Add setup method and Setting object to configure AMS

lib/active_model/serializer/settings.rb

@@ -0,0 +1,27 @@
+module ActiveModel
+  class Serializer
+    class Settings
+      def initialize
+        @data = {}
+      end
+
+      def [](key)
+        @data[key.to_s]
+      end
+
+      def []=(key, value)
+        @data[key.to_s] = value
+      end
+
+      def each(&block)
+        @data.each(&block)
+      end
+
+      def clear
+        @data.clear
+      end
+    end
+
+    SETTINGS = Settings.new
+  end
+end