Introduce singleton types

Just for future, as this gives us a way to know immediately in the type, which represent normal, and which singleton classes
Also instantiate singleton class lazily (with singleton type)
This makes the type of class single, ie unique, immediately when it is used, ie methods or variables defined.
Fixes a design mistake, where all singletonn classes shared the same type, and thus unique methods per class were impossible
(Also some misc in commit)

lib/risc/parfait_boot.rb

@@ -29,7 +29,7 @@ module Parfait
     space = Space.new( )
     type_names.each do |name , ivars |
       ivars[:type] = :Type
-      instance_type = Type.new(name , ivars)
+      instance_type = Type.new(name , ivars , 0)
       space.add_type instance_type
       space.classes[name] = Class.new(name , nil , instance_type)
     end
@@ -51,7 +51,6 @@ module Parfait
     classes.each do |name , cl|
       object_type = Parfait.object_space.get_type_by_class_name(name)
       raise "nil type" unless object_type
-      cl.single_class.instance_eval{ @instance_type = class_type}
       cl.instance_eval{ @instance_type = object_type}
       cl.instance_eval{ @super_class_name = super_names[name] || :Object}
       object_type.instance_eval{ @object_class = cl }
@@ -140,7 +139,8 @@ module Parfait
               true_object: :TrueClass, false_object: :FalseClass , nil_object: :NilClass},
       TrueClass: {},
       Type: {names: :List , types: :List  ,
-             object_class: :Class, methods: :CallableMethod } ,
+             object_class: :Class, methods: :CallableMethod ,
+             is_single: :Object} ,
       VoolMethod: { name: :Word , args_type: :Type , frame_type: :Type } ,
       Word: {char_length: :Integer , next_word: :Word} ,
       }