Add an `AUTHORS` file and update copyright notices.

Change-Id: Ifb505e5664996c1af41e38376e58ba49864213a3
diff --git a/tools/clang_format.py b/tools/clang_format.py
index d838cab..12a14be 100755
--- a/tools/clang_format.py
+++ b/tools/clang_format.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python2.7
 
-# Copyright 2016, ARM Limited
+# Copyright 2016, VIXL authors
 # All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without