enforces data encapsulation in vool tree

gets rid of attraccessor

lib/vool/send_statement.rb

@@ -1,9 +1,9 @@
 module Vool
   class SendStatement < Statement
-    attr_accessor :name , :receiver , :arguments
-    def initialize(name)
-      @name = name
-      @arguments = []
+    attr_reader :name , :receiver , :arguments
+
+    def initialize(name , receiver , arguments = [])
+      @name , @receiver , @arguments = name , receiver , arguments
     end
   end
 end