Wrapping block elements in <a>

Tidy does not like it when I wrap block-level elements in anchor tags:

```
<a>
  <div>
    <p>Tidy says "inserting implicit <a>"</p>
  </div>
</a>
```

tidy -v: HTML Tidy for Mac OS X version 4.9.15

Anchor wrapping is new in HTML5, see http://html5doctor.com/block-level-links-in-html-5/
