Add some documentation and a todo for enum.c

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@17530 65c4cc65-6c06-0410-ace0-fbb531ad65f3

enum.c

@@ -35,6 +35,9 @@
  * - ENUM SIP: http://www.ietf.org/rfc/rfc3764.txt
  * - IANA ENUM Services: http://www.iana.org/assignments/enum-services
  *
+ * \par Possible improvement
+ * \todo Implement a caching mechanism for multile enum lookups
+ * - See http://bugs.digium.com/view.php?id=6739
  */
 
 #include <sys/types.h>