fix even more broken markdown links

Added `bin/find-missing-links.sh` tool to check for
markdown links to missing local files.

Regarding the missing link tool:

```
    Here be extended regular expression magic dragons! :-)
```

Added `make find_missing_links` to the top level Makefile.

Added `make find_missing_links` to `make www` and `make quick_www`.

Ran `make www` to perform the above.

TODO: Fix markdown links to missing local files.

2001/index.html

@@ -412,7 +412,7 @@ them for the next IOCCC.</p>
 <p>We believe you will be impressed with this year’s winning entries The <a href="ollinger/index.html">Best of
 Show</a> is a fine example of obfuscation. But don’t ignore
 the other entries! There are games, programs that speak, ones that compile code
-and <a href="2001/anonymous/index.html">one that <em>might</em> run binaries you already have</a>.</p>
+and <a href="anonymous/index.html">one that <em>might</em> run binaries you already have</a>.</p>
 <p>The <a href="bellard/index.html">Best/Worst Abuse of the Rules</a> is technically allowed by the
 <a href="rules.txt">rules</a>. This year we awarded it again, but don’t assume you can get
 away with using the same technique next time … :-)</p>