Rename Vool to Sol

Simple is really the descriptive name for the layer
Sure, it is "virtual" but that is not as important as the fact that it is simple (or simplified)
Also objct (based really) is better, since orientated implies it is a little like that, but only orientated, not really it. Sol only has objects, nothing else
Just cause i was renaming anyway

lib/parfait/space.rb

@@ -111,7 +111,7 @@ module Parfait
     # The superclass must be known when the class is created, or it raises an error.
     # The class is initiated with the type of the superclass (hence above)
     #
-    # Only Vool::ClassExpression really ever creates classes and "grows" the type
+    # Only Sol::ClassExpression really ever creates classes and "grows" the type
     # according to the instances it finds, see there
     #
     def create_class( name , superclass = nil )