rename blocks do_add to be the same as sunctions add_code to blur the difference

lib/vm/values/reference.rb

@@ -1,9 +1,11 @@
 module Vm
   class Reference < Word
     # needs to be here as Word's constructor is private (to make it abstract)
-    def initialize reg
-      super
+    def initialize reg , clazz = nil
+      super(reg)
+      @clazz = clazz
     end
+    attr_accessor :clazz
 
   end
 end