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.

2019/lynn/index.html

@@ -464,8 +464,8 @@ of the characters <code>a</code> and <code>b</code> that contain an even number
 <p>A GHC wrapper is provided:</p>
 <pre><code>    ghc ghclol.hs</code></pre>
 <h3 id="strongly-connected-components">Strongly-connected components:</h3>
-<p>See <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2019/lynn/scc.hs">scc.hs</a> (and its GHC wrapper <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2019/lynn/ghcscc.hs">ghcscc.hs</a>) for an elegant
-way to print the strongly-connected components of a graph in reverse topological
+<p>See <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2019/lynn/scc.hs">scc.hs</a>, and its GHC wrapper <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2019/lynn/ghcscc.hs">ghcscc.hs</a>,
+for an elegant way to print the strongly-connected components of a graph in reverse topological
 order.</p>
 <pre><code>    (./prog &lt; scc.hs ; cat prog.c) &gt; scc.c</code></pre>
 <p>It expects the input to be in a similar format as a previous entry
@@ -545,8 +545,8 @@ format earlier in the source.)</li>
 ternary operators, and so on.</li>
 <li>Huffman coding.</li>
 <li>Base-85 because high bits are frowned upon.</li>
-<li>Mixed radix encoding to game iocccsize. From a past entry
-(<a href="../../2018/bellard/index.html">2018/bellard</a>), it seems 9 11 12 32 are the only
+<li>Mixed radix encoding to game iocccsize. From a past entry,
+<a href="../../2018/bellard/index.html">2018/bellard</a>, it seems 9 11 12 32 are the only
 whitespace octets that may appear verbatim in string literals.</li>
 <li>Choosing what to encode in Huffman/base-85 and what to encode in mixed radix
 was a delicate balancing act. In the end, I only had a few bytes to spare, which
@@ -554,7 +554,7 @@ I spent on gratuitous confusion.</li>
 <li>The effects of some functions depend on the order their arguments are
 evaluated, yet the program works either way. Why?</li>
 <li>Ugly macros for the runtime system’s jump table for lazy reduction. A previous
-entry (<a href="../../2013/endoh1/index.html">2013/endoh1</a>) has a cuter solution, which I
+entry, <a href="../../2013/endoh1/index.html">2013/endoh1</a>, has a cuter solution, which I
 avoid because of originality concerns and also because my combinators are
 compressed.</li>
 <li>Relies on the inability of C comments to nest.</li>