replace obsolete a name tags with div

This HTML is now obsolete in HTML 5:

```html
<a name="faq0"></a>Section 0: Submitting entries to a new IOCCC
```

Instead we need to use the div HTML elements:

```html
<div id="faq0">Section 0: Submitting entries to a new IOCCC</div>
```

We are testing a fix for the top level HTML files.

Run `make gen_top_html` to perform the above and test under macOS.

TODO: Apply this type of fix across the entire web site if all is well.

contact.md

@@ -36,7 +36,7 @@ and suggestion in the relevant places.
 See the above FAQ entries for more details.
 
 
-# <a name="mastodon"></a>Try mastodon
+# <div id="mastodon">Try mastodon</div>
 
 You may wish to follow us [IOCCC on Mastodon](https://fosstodon.org/@ioccc)
 as we use that platform to announce things such as the opening of a new IOCCC