title: Instagram-style navigation bar hiding
body: <p>I need to hide the navigation bar when the user scrolls down. Currently, I'm calling <code>setNavigationBarHidden: YES animated:YES</code> on scroll, but this solution isn't ideal as it makes the main view jump up as soon as the animation is called. </p>
  
  <p>The Instagram app has a much better solution - the navigation bar is locked to the top of the main view, and it scrolls up as the user scrolls. Scroll down a few pixels, and only part of the nav bar gets hidden.</p>
  
  <p>Any ideas on how this could be accomplished?</p>