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.

2012/endoh2/index.html

@@ -421,7 +421,7 @@ machine</a> emulation?</p>
 <p>Yeah, “Again”. Sorry. But I don’t feel guilty or uncomfortable.</p>
 <p>This entry is based on ‘over-used themes’ such as self reproducing
 program and <a href="https://en.wikipedia.org/wiki/Pi">pi</a> or
-<a href="https://en.wikipedia.org/wiki/E_(mathematical_constant)">e</a>) computation. I
+<a href="https://en.wikipedia.org/wiki/E_(mathematical_constant(">e</a> computation. I
 know you’re tired of them.</p>
 <p>But have you ever seen them <strong>all-in-one</strong>?</p>
 <h3 id="what-it-is">What it is</h3>
@@ -436,7 +436,7 @@ know you’re tired of them.</p>
 </ul>
 <p>One more thing… When you give a command line argument <code>e</code> to the
 first program, the generated one will compute <a href="https://en.wikipedia.org/wiki/E_(mathematical_constant)">Napier’s
-constant</a>)
+constant</a>
 rather than pi.</p>
 <h3 id="obfuscation">Obfuscation</h3>
 <p>This program itself is in the shape of a