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.

1992/buzzard.2/index.html

@@ -484,7 +484,7 @@ tackle this project.</p>
 <p><code>first</code> is reasonably portable. You may need to adjust the size of the buffers
 on smaller machines; <code>m[]</code> needs to be at least 2000 long, though.</p>
 <p>I say <code>first</code> is portable mainly because it uses native types. Unlike
-[FORTH](https://en.wikipedia.org/wiki/Forth_(programming_language), which
+<a href="https://en.wikipedia.org/wiki/Forth_(programming_language)">FORTH</a>, which
 traditionally allows byte and multi-byte operations, all operations are
 performed on C <code>int</code>s. That means <code>first</code> code is only as portable as the same
 code would be in C. As in C, the result of dividing <code>-1</code> by <code>2</code> is machine (or