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/deckmyn/README.md

@@ -108,8 +108,8 @@ be `"`` ` ``cat deckmyn.c`` ` ``"`.
 The second command line argument is the music itself. This is, again, a string,
 not a file name. All music signs are entered as tokens of exactly 3 characters.
 The code is very sensitive to bad spacing! So for instance, if you use a file to
-write the music (e.g. [example\_greensleeves](%%REPO_URL%%/2012/deckmyn/example_greensleeves)), you should
-keep in mind that newline is also a character!
+write the music (e.g., [example\_greensleeves](%%REPO_URL%%/2012/deckmyn/example_greensleeves) file),
+you should keep in mind that newline is also a character!
 
 
 ### Internals

2012/deckmyn/index.html

@@ -452,8 +452,8 @@ be <code>"``</code> <code>cat deckmyn.c</code> <code>``"</code>.</p>
 <p>The second command line argument is the music itself. This is, again, a string,
 not a file name. All music signs are entered as tokens of exactly 3 characters.
 The code is very sensitive to bad spacing! So for instance, if you use a file to
-write the music (e.g. <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2012/deckmyn/example_greensleeves">example_greensleeves</a>), you should
-keep in mind that newline is also a character!</p>
+write the music (e.g., <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2012/deckmyn/example_greensleeves">example_greensleeves</a> file),
+you should keep in mind that newline is also a character!</p>
 <h3 id="internals">Internals</h3>
 <p>To minimise the memory footprint, this program has <em>no variable declarations at
 all</em>, except for the arguments to <code>main()</code>. The only available memory space is