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/README.md

@@ -39,7 +39,7 @@ them for the next IOCCC.
 We believe you will be impressed with this year's winning entries  The [Best of
 Show](ollinger/index.html) is a fine example of obfuscation.  But don't ignore
 the other entries!  There are games, programs that speak, ones that compile code
-and [one that _might_ run binaries you already have](2001/anonymous/index.html).
+and [one that _might_ run binaries you already have](anonymous/index.html).
 
 The [Best/Worst Abuse of the Rules](bellard/index.html) is technically allowed by the
 [rules](rules.txt).  This year we awarded it again, but don't assume you can get