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

test/ruby/test_class_statement3.rb

@@ -11,7 +11,7 @@ module Ruby
       assert_equal 4 , @vool.body.length , "2 setters, 2 getters"
     end
     def test_setter
-      assert_equal Vool::MethodStatement , setter.class
+      assert_equal Vool::MethodExpression , setter.class
     end
     def test_setter_assign
       assert_equal Vool::Statements , setter.body.class