improved indentation and whitespace for markdown code blocks

All code blocks in markdown have been intended by at least 4 spaces.

We add `--tab-stop=8` to all `pandoc(1)` executions in order to set
a better tab stop indentation, especially for tab intended code blocks.

Changed `bin/pandoc-wrapper.sh` VERSION from "1.5.3 2024-03-26"
to "1.6 2024-03-31".

Fixed `1991/brnstnd/sorta.README.md` so that the sorta code
is code blocks.

Removed unneeded paragraph group in copyright in `inc/footer.default.html`.

Fixed excess whitespace after list Author on entry `index.html` page.

Changed `bin/output-index-author.sh` VERSION from "1.5.2 2024-03-26"
to "1.6 2024-03-31".

Performed `make www` to perform the above and test under macOS.

TODO: Fix the problem of the initial line of code being extra intended.
TODO: Fix excess whitespace around code that is inline.

2001/index.html

@@ -172,7 +172,7 @@ we do look at and work out what every entry does.</p>
 <p>Please send us comments and suggestions what we have expressed above.
 Also include anything else that you would like to see in future contests.
 Send such email to:</p>
-<pre><code>questions@ioccc.org</code></pre>
+<pre><code>    questions@ioccc.org</code></pre>
 <p><strong>IMPORTANT NOTE</strong>: The email addresses found above are for historical
 purposes only, and should not be used today. See
 <a href="../contact.html">contact.html</a> for up to date contact details