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/crazy.log.md

@@ -117,3 +117,18 @@ But did you see anything strange? The bug is on the fourth line below the upper
 However it appears to be inside the body of the snake! But actually that's just where
 the snake split off at some point: the snake no longer occupies that place and indeed I
 could safely go through that part of the screen.
+
+
+<!--
+
+    Copyright © 1984-2024 by Landon Curt Noll. All Rights Reserved.
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+    You are free to share and adapt this file under the terms of this license:
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+	Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
+
+    For more information, see:
+
+	https://creativecommons.org/licenses/by-sa/4.0/
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+-->