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/ferguson1/index.html

@@ -495,7 +495,7 @@ This game has a number of configurable pitfalls including walls and snakes.</p>
 </ul>
 <p>Workarounds for various game <em>features</em></p>
 <ul>
-<li><a href="%5Bbugs.html">bugs.html</a></li>
+<li><a href="bugs.html">bugs.html</a></li>
 </ul>
 <p>Bugs and things that might seem like bugs but are not.</p>
 <ul>
@@ -818,7 +818,7 @@ been warned.</li>
 additional obfuscation technique (see spoilers) but it also has more digraphs
 and as the judges said they feel that digraphs are dated so that’s probably why
 they chose the first layout. The <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2020/ferguson1/prog.3-j.c">prog.3-j.c</a> version is
-<a href="https://github.com/ioccc-src/temp-test-ioccc/blob/masterhttps://github.com/ioccc-src/temp-test-ioccc/blob/master/2020/ferguson1/prog.3.c">prog.3.c</a> with a shorter <code>J</code> macro.</p>
+<a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2020/ferguson1/prog.3.c">prog.3.c</a> with a shorter <code>J</code> macro.</p>
 <p>The prog.alt.c version is the one that allows for customising the bug colour and
 it’s used in both <a href="snake-colours.sh">snake-colours.sh</a> and <a href="play.sh">play.sh</a>. It also calls <code>erase()</code>
 first, clearing the screen, which the play.sh and snake-colours.sh scripts also