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/zeitak/README.md

@@ -31,7 +31,7 @@ will not detect multiple issues.
 
 ## Alternate code:
 
-The alternate code, [zeitak.alt.c](z%%REPO_URL%%/2012/zeitak/eitak.alt.c), is a version that was slightly
+The alternate code, [zeitak.alt.c](%%REPO_URL%%/2012/zeitak/zeitak.alt.c), is a version that was slightly
 deobfuscated by the author. You may find reading it helpful in your attempt to
 understand this extremely subtle entry.
 

2012/zeitak/index.html

@@ -411,7 +411,7 @@ text files that are not code.</p>
 <p>NOTE: the program prints an error and exits on the first nesting error so it
 will not detect multiple issues.</p>
 <h2 id="alternate-code">Alternate code:</h2>
-<p>The alternate code, <a href="zhttps://github.com/ioccc-src/temp-test-ioccc/blob/master/2012/zeitak/eitak.alt.c">zeitak.alt.c</a>, is a version that was slightly
+<p>The alternate code, <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2012/zeitak/zeitak.alt.c">zeitak.alt.c</a>, is a version that was slightly
 deobfuscated by the author. You may find reading it helpful in your attempt to
 understand this extremely subtle entry.</p>
 <h3 id="alternate-build">Alternate build:</h3>