goprotobuf: Use a standard redirecting AUTHORS and CONTRIBUTORS file.

Correct copyright notice to "The Go Authors" throughout.

R=rsc, bradfitz
CC=golang-dev
http://codereview.appspot.com/6845101
diff --git a/AUTHORS b/AUTHORS
new file mode 100644
index 0000000..15167cd
--- /dev/null
+++ b/AUTHORS
@@ -0,0 +1,3 @@
+# This source code refers to The Go Authors for copyright purposes.
+# The master list of authors is in the main Go distribution,
+# visible at http://tip.golang.org/AUTHORS.