updates AUTHORS and generator script

tools/update-authors.sh

@@ -25,8 +25,12 @@ END {
   print "# Authors ordered by first contribution.\n";
   print "# Generated by tools/update-authors.sh\n";
   print "\n", @authors;
-  print "\n*** = works in the public domain";
+  print "\n*** some works are in the public domain, all others licensed under terms: see LICENSE";
 
 }
 
 '
+
+echo "\n\nSome commits are co-authored:\n"
+
+git log | grep Co-Author