Renaming Vool exppressions rightly

Class, Method and Lambda (was block) are expressions.
Just making things clearer, especially for the blocks (ahem, lambdas) is matters.
wip

lib/ruby/class_statement.rb

@@ -29,7 +29,7 @@ module Ruby
           meths += transform_statement(meth)
         end
       end
-      Vool::ClassStatement.new(@name , @super_class_name, Vool::Statements.new(meths) )
+      Vool::ClassExpression.new(@name , @super_class_name, Vool::Statements.new(meths) )
     end
 
     # We rewrite certain send statements (so raise error for all else)