title: Event to detect when position:sticky is triggered
body: <p>I'm using the new <code>position: sticky</code> (<a href="http://updates.html5rocks.com/2012/08/Stick-your-landings-position-sticky-lands-in-WebKit" rel="noreferrer">info</a>) to create an iOS-like list of content.</p>
  <p>It's working well and far superior than the previous JavaScript alternative (<a href="http://jsbin.com/omanut/2/edit" rel="noreferrer">example</a>) however as far as I know no event is fired when it's triggered, which means I can't do anything when the bar hits the top of the page, unlike with the previous solution.</p>
  <p><strong>I'd like to add a class (e.g. <code>stuck</code>) when an element with <code>position: sticky</code> hits the top of the page. Is there a way to listen for this with JavaScript? Usage of jQuery is fine.</strong></p>