fix and test vool return statement

lib/vool/compiler.rb

@@ -99,9 +99,8 @@ module Vool
     end
 
     def on_return statement
-      w = ReturnStatement.new()
-      w.return_value = process(statement.children.first)
-      w
+      return_value = process(statement.children.first)
+      ReturnStatement.new( return_value )
     end
 
     def on_function  statement

lib/vool/return_statement.rb

@@ -1,5 +1,9 @@
 module Vool
   class ReturnStatement < Statement
     attr_accessor :return_value
+
+    def initialize(value)
+      @return_value = value
+    end
   end
 end