improve the footer of HTML files

We improve the `inc/footer.default.html` file to make
the _Copyright and CC BY-SA 4.0 License_ clear.

We add `license.md` and generate `license.html` (via `make
gen_top_html`) so that key features and terms of the _Copyright and
CC BY-SA 4.0 License_ are accessible.

Add CC BY-SA 4.0 license images into the `png/` directory.

FYI: We use the license to allow the open use of IOCCC entry code,
and at the same time, we help ensure that those working on the IOCCC
have proper Attribution including, of course, the IOCCC winners
themselves!  The _Copyright and CC BY-SA 4.0 License_ help ensure
that everyone may enjoy the IOCCC.

Added '#copyright' to all generated HTML pages so that the
_Copyright and CC BY-SA 4.0 License_ may be reached.

Changed `bin/gen-top-html.sh` VERSION from "1.2.2 2024-03-26"
to "1.2.3 2024-04-12".

Fix `bin/gen-sitemap.sh` to remove requirement of `ioccc.tar.bz2`.

Changed `bin/gen-sitemap.sh` VERSION from "1.3.4 2024-03-27"
to "1.3.5 2024-04-13".

Perform `make www sitemap` to perform the above.

We also give a _hint_ as to the next project.

TODO: Complete that next project we are _hinting_ at.

TODO: Review the work being done by a web designer to see
      how their work might be incorporated into the web site.

1988/robison/index.html

@@ -232,14 +232,30 @@ ANSI committee should look into this practical simplification of C.</p>
 -->
 
 <div class="footer">
-  <h2>Copyright and CC BY-SA 4.0 License</h2>
-  <p>This file and web page is:</p>
-  <blockquote><b>Copyright &copy; 1984-2024 by Landon Curt Noll. All Rights Reserved.</b></blockquote>
-  <p>You are free to share and adapt this file under the terms of this license:</p>
-  <blockquote><b>Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)</b></blockquote>
-  <p>For more information, see:</p>
-  <blockquote><a
-    href="https://creativecommons.org/licenses/by-sa/4.0/">https://creativecommons.org/licenses/by-sa/4.0/</a></blockquote>
+  <h2><a name="copyright"></a>Copyright and CC BY-SA 4.0 License</h2>
+  <p>All IOCCC content including this file and web page are:</p>
+  <b>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Copyright &copy; 1984-2024 by Landon Curt Noll. <a href="https://creativecommons.org/faq/#what-does-some-rights-reserved-mean">Some Rights Reserved</a>.</b>
+  <p>This work is licensed by Landon Curt Noll under:</p>
+  <p xmlns:cc="http://creativecommons.org/ns#" ><b><a href="https://creativecommons.org/licenses/by-sa/4.0/?ref=chooser-v1"
+  target="_blank" rel="license noopener noreferrer" style="display:inline-block;">&nbsp;&nbsp;&nbsp;&nbsp;CC BY-SA 4.0
+  <img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
+  src="../..//svg/cc.svg"
+  alt="cc inside circle symbol">
+  <img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
+  src="../..//svg/by.svg"
+  alt="person inside circle symbol">
+  <img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
+  src="../..//svg/sa.svg"
+  alt="arrow looping back on itself inside circle symbol">
+  </a></b></p>
+  <p>The <b>CC BY-SA 4.0 LEGAL CODE</b> for this license is found under:</p>
+  <p>&nbsp;&nbsp;&nbsp;<b><a href="https://creativecommons.org/licenses/by-sa/4.0/legalcode.en">
+  https://creativecommons.org/licenses/by-sa/4.0/legalcode.en</a></b></p>
+  <p>You should <b>carefully review</b> all of the terms and conditions of the
+  <a href="https://creativecommons.org/licenses/by-sa/4.0/legalcode.en">actual license</a>
+  before using the licensed material.</p>
+  <p>You may wish to review the <b><a href="../../license.html">highlights of some of the key
+  features and terms</a></b> of the <a href="https://creativecommons.org/licenses/by-sa/4.0/legalcode.en">actual license</a>.</p>
   <h2>Coda</h2>
   <p><a href="https://validator.w3.org/nu/?doc=https%3A%2F%2Fioccc-src.github.io%2Ftemp-test-ioccc%2F1988%2Frobison%2Findex.html">Nu HTML check this web page</a></p>
   <p><a href="#top">Jump to top</a> <a href="#content">Jump to Content</a> <a href="#inventory">Jump to Inventory</a></p>