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/return_statement.rb

@@ -5,7 +5,7 @@ module Ruby
     attr_reader :return_value
 
     def initialize(value)
-      @return_value = value || NilConstant.new 
+      @return_value = value || NilConstant.new
     end
 
     def to_vool