improve Copyright and CC

The inc/footer.default.html now has a common Copyright and CC BY-SA
4.0 License section for all generated HTML files.

All markdown files have a similar Copyright and CC
at the bottom in the form of an HTML comment.

2020/ferguson1/bugs.md

@@ -321,10 +321,17 @@ but it is very much appreciated and it means a great deal to me. Cheers.)
 [spoilers]: spoilers.markdown
 [screenshot of halfwidth vs fullwidth]: halfwidth_vs_fullwidth.png
 
------------------------------------------------------------------------------------------------------
-(c) Copyright 1984-2020, [Leo Broukhis, Simon Cooper, Landon Curt Noll][judges] - All rights reserved
-This work is licensed under a [Creative Commons Attribution-ShareAlike 3.0 Unported License][cc].
 
-[judges]: https://www.ioccc.org/judges.html
-[cc]: http://creativecommons.org/licenses/by-sa/3.0/
------------------------------------------------------------------------------------------------------
+<!--
+
+    Copyright © 1984-2024 by Landon Curt Noll. All Rights Reserved.
+
+    You are free to share and adapt this file under the terms of this license:
+
+	Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
+
+    For more information, see:
+
+	https://creativecommons.org/licenses/by-sa/4.0/
+
+-->