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.

2018/burton1/index.html

@@ -426,7 +426,7 @@ It adds several nice-to-have features, and allows salt-to-taste customizability.
 <li>X86-Linux, gcc 4.1.2 and 4.8.4, -O0 and -O3</li>
 <li>ARM-QEMU, gcc 4.8.4, -O0 and -O3</li>
 <li>X86-FreeBSD 10.3, clang 3.4.1, -O0 and -O3</li>
-<li>TCC 0.9.26 (x86-64) (used as a proxy for <a href="../../2001/bellard/index.html">2001/bellard</a>)</li>
+<li>TCC 0.9.26 (x86-64), used as a proxy for <a href="../../2001/bellard/index.html">2001/bellard</a></li>
 <li>UNIX V7 pcc (Johnson’s C compiler) on a <a href="http://simh.trailing-edge.com/">simulated PDP-11/45</a>
 (see spoiler for further detail)</li>
 </ul>
@@ -526,7 +526,7 @@ that writing more than a single char will cause a fault, which is <em>technicall
 correct.</p>
 <p>But how does this work at all, even as an extension? <code>o[]</code> allocates one(!)
 byte in a zero-filled data area (formerly
-<a href="https://en.wikipedia.org/wiki/.bss">BSS</a>). The UNIX-derived systems this code
+<a href="https://en.wikipedia.org/wiki/.bss">.bss</a> language). The UNIX-derived systems this code
 was run upon all place the storage of <code>O</code> and <code>o</code> into a zero-filled VM page
 with nothing following: thus, there are plenty of available and unused zero
 bytes following <code>O</code>, addressed via <code>o</code>, and this code only needs 17. This is