Adding myself to AUTHORS/CONTRIBUTORS as a result of https://golang.org/cl/156079

R=golang-dev, rsc
CC=r
https://golang.org/cl/157072
diff --git a/AUTHORS b/AUTHORS
index bada5e7..29cc62b 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -20,6 +20,7 @@
 Josh Goebel <dreamer3@gmail.com>
 Google Inc.
 Kevin Ballard <kevin@sb.org>
+Michael Elkins <michael.elkins@gmail.com>
 Michael Hoisie <hoisie@gmail.com>
 Môshe van der Sterre <moshevds@gmail.com>
 Sergio Luis O. B. Correia <sergio@larces.uece.br>