make the <a> tag the parent of the target to add hrefs to everything

This is a fix for the following sprout:
http://www.share-elm.com/sprout/53b117d1e4b07afa6f982635

As first noticed by Do Bi.

I tried to keep this change pixel perfect but there may be a weird case I overlooked. See if you can break this.
I specifically mean the line `a.style.position = 'relative`. What is that doing?