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.

1987/lievaart/README.md

@@ -29,7 +29,7 @@ We believe that you too will be amazed at just how much power Mr. Lievaart
 packed into 1024 bytes!
 
 This Plays the game of [Reversi
-(Othello)](https://en.wikipedia.org/wiki/Reversi)!  Compile and run.  It then
+[Othello](https://en.wikipedia.org/wiki/Reversi)!  Compile and run.  It then
 asks for a playing level. Enter 0-10 (easy-hard).  It then asks for
 your move. A move is a number within 11-88, or 99 to pass.  Illegal
 moves (except for an illegal pass) are rejected.  Then the computer

1987/lievaart/index.html

@@ -409,8 +409,8 @@ Location: <a href="../../location.html#NL">NL</a> - <em>Kingdom of the Netherlan
 <h2 id="judges-remarks">Judges’ remarks:</h2>
 <p>We believe that you too will be amazed at just how much power Mr. Lievaart
 packed into 1024 bytes!</p>
-<p>This Plays the game of <a href="https://en.wikipedia.org/wiki/Reversi">Reversi
-(Othello)</a>! Compile and run. It then
+<p>This Plays the game of [Reversi
+<a href="https://en.wikipedia.org/wiki/Reversi">Othello</a>! Compile and run. It then
 asks for a playing level. Enter 0-10 (easy-hard). It then asks for
 your move. A move is a number within 11-88, or 99 to pass. Illegal
 moves (except for an illegal pass) are rejected. Then the computer