Added self to AUTHORS and CONTRIBUTORS.

R=rsc
https://golang.org/cl/154128
diff --git a/AUTHORS b/AUTHORS
index 8c01349..3b9074f 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -8,6 +8,7 @@
 
 # Please keep the list sorted.
 
+Abhinav Gupta <abhinav.g90@gmail.com>
 David Titarenco <david.titarenco@gmail.com>
 Google Inc.
 Kevin Ballard <kevin@sb.org>