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/parfait/vool_method.rb

@@ -20,6 +20,7 @@ module Parfait
       @args_type = args_type
       @frame_type = frame_type
       @source = source
+      #raise source.to_s if name == :type_length
       raise "Name must be symbol" unless name.is_a?(Symbol)
       raise "args_type must be type" unless args_type.is_a?(Parfait::Type)
       raise "frame_type must be type" unless frame_type.is_a?(Parfait::Type)