fix more broken markdown links

We fix more markdown links in markdown files that refer to files
internally to the web site.

Added tmp tools to find and print various markdown links:

* `tmp/md-links.sh` - print all markdown links
* `tmp/md-token-links.sh` - print all markdown links that start with a **%%TOKEN%%**
* `tmp/md-local-links.sh` - print all markdown links to a local file
* `tmp/md-link-paths.sh` - print local file paths referenced in markdown links

Fixed a number of markdown formatting problems with `thanks-for-help.md`.
Fixed markdown links to files in `thanks-for-help.md`.  Improved
heading levels in `thanks-for-help.md`, and made entry sections consistent.

Changed all markdown links that end in "))" to end in a better way.

Explained in `markdown.md` why we are avoiding markdown links that
end in "))".

Ran `make www` to perform the above.

TODO: Fix stuff we broke by mistake doing the above.

TODO: Fix more broken markdown links.

2020/giles/index.html

@@ -420,7 +420,7 @@ will be converted to the DTMF sound!</p>
     ./prog 867-5309 &gt; jenny.wav</code></pre>
 <p>If the script <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2020/giles/try.sh">try.sh</a> did not play a WAV file, it means you do not have
 SoX installed; see <a href="../../faq.html#sox">FAQ 3.10: How do I compile and use an IOCCC entry that
-requires sound?</a>). In this case install it and try it again or
+requires sound?</a>. In this case install it and try it again or
 play the files <code>jenny.wav</code> and <code>ioccc28.wav</code> in a program that can play WAV
 files.</p>
 <p>NOTE: the phone number of <code>jenny.wav</code> comes from