move return address generation to factory

removes the list from space
adds a ReturnAddress factory instead
and uses these throughout

lib/risc/instructions/label.rb

@@ -65,7 +65,7 @@ module Risc
   # An integer is plucked from object_space abd added to the machine constant pool
   # if none was given
   def self.label( source , name , position = nil , nekst = nil)
-    position = Parfait.object_space.get_address unless position
+    position = Parfait.object_space.get_next_for(:ReturnAddress) unless position
     Label.new( source , name , position, nekst )
   end
 end

lib/risc/parfait_boot.rb

@@ -160,12 +160,11 @@ module Parfait
       NamedList: {},
       NilClass: {},
       Object: {},
-      Factory: { for_type: :Type , next_object: :Object , last_object: :Object ,
+      Factory: { for_type: :Type , next_object: :Object ,
               reserve: :Object , attribute_name: :Word },
       ReturnAddress: {next_integer: :ReturnAddress},
       Space: {classes: :Dictionary , types: :Dictionary , factories: :Dictionary,
               next_message: :Message , messages: :Message ,
-              next_address: :ReturnAddress ,addresses: :ReturnAddress ,
               true_object: :TrueClass, false_object: :FalseClass , nil_object: :NilClass},
       TrueClass: {},
       Type: {names: :List , types: :List  ,