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/index.html

@@ -421,7 +421,7 @@ very likely say <a href="http://bit.ly/R6ALpK">wow</a> as we did!</p></li>
 <p>But don’t ignore the other winning entries! There are games, utilities,
 eye candy, calculators and graphical tools to explore.</p>
 <p>This year, Yusuke Endoh won with two entries, one of which
-(<a href="endoh1/index.html">endoh1</a>) won the special Honorable mention award. Eight of
+(<a href="endoh1/index.html">endoh1</a> entry) won the special Honorable mention award. Eight of
 the winning entries were from people who won in previous years.</p>
 <p>This year we had a number of authors from Asia. We saw our second
 authors from China and first from Korea. We are pleased to see