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.

2005/aidan/README.md

@@ -111,7 +111,7 @@ it as you wish, though please give me credit.
 ### What is a sudoku?
 
 (If you know, feel free to skip this section. Get more details from [the
-wikipedia entry](http://en.wikipedia.org/wiki/Sudoku))
+wikipedia entry](http://en.wikipedia.org/wiki/Sudoku).
 
 A sudoku is a type of logic puzzle. You are given a grid of 9x9 boxes, some
 of which contain digits. This is divided into a 3x3 set up, e.g. (from the
@@ -177,7 +177,7 @@ program generated):
 ```
 
 Be warned - it's evil! (I certainly haven't been able to solve it by hand. The
-brute-force program given above, `sudoku-bfi.c` ([aidan.alt.c](%%REPO_URL%%/2005/aidan/aidan.alt.c)),
+brute-force program given above, `sudoku-bfi.c`, [aidan.alt.c](%%REPO_URL%%/2005/aidan/aidan.alt.c),
 also has trouble - it took 66 seconds to solve it - but probably for different
 reasons. That's the worst performance I've had from brute-force so far!)