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.

2015/burton/README.md

@@ -122,7 +122,7 @@ Flow control is by `for` and `return`.  It is `if`-less,  `switch`-less,
 `while`-less, and hopeless. Literally, if not figuratively. ;-)
 
 The code size is intentionally 2015, as stated by `iocccsize -i`, and can be
-reformatted without changes (as in [rule2.c](%%REPO_URL%%/2015/burton/rule2.c)) to exactly 4096 octets.
+reformatted without changes (as in [rule2.c](%%REPO_URL%%/2015/burton/rule2.c) source) to exactly 4096 octets.
 
 Finally, `calc` is interesting, if for no other reason than it is practically
 useful: Hex/decimal conversion, arithmetic, byte-swapping, bit-shifting, and

2015/burton/index.html

@@ -454,7 +454,7 @@ and hex input.</p>
 <p>Flow control is by <code>for</code> and <code>return</code>. It is <code>if</code>-less, <code>switch</code>-less,
 <code>while</code>-less, and hopeless. Literally, if not figuratively. ;-)</p>
 <p>The code size is intentionally 2015, as stated by <code>iocccsize -i</code>, and can be
-reformatted without changes (as in <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/burton/rule2.c">rule2.c</a>) to exactly 4096 octets.</p>
+reformatted without changes (as in <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/burton/rule2.c">rule2.c</a> source) to exactly 4096 octets.</p>
 <p>Finally, <code>calc</code> is interesting, if for no other reason than it is practically
 useful: Hex/decimal conversion, arithmetic, byte-swapping, bit-shifting, and
 logical operations with memory, on the command line, or interactively.</p>