renamed true,false,nil class to constant (from value)

lib/register/integer.rb

@@ -1,5 +1,5 @@
 module Register
-  class Integer < Word
+  class UnusedAndAbandonedInteger < Word
     # needs to be here as Word's constructor is private (to make it abstract)
     def initialize reg
       super

lib/virtual/constants.rb

@@ -2,11 +2,11 @@ module Virtual
   
   class Constant < ::Virtual::Value
   end
-  class TrueValue < Constant
+  class TrueConstant < Constant
   end
-  class FalseValue < Constant
+  class FalseConstant < Constant
   end
-  class NilValue < Constant
+  class NilConstant < Constant
   end
 
   # another abstract "marker" class (so we can check for it)