title: bootstrap nav affix w/ animation (slidedown/slideup)
body: <p>Looking to create a navigation that behaves like the nav on <a href="http://www.invisionapp.com/" rel="nofollow">http://www.invisionapp.com/</a></p>
  
  <p>The following code causes my nav to slide down after crossing the <code>data-offset-top</code> position (while scrolling down the page), but I can't figure out how to slide the nav back up when crossing the <code>data-offset-top</code> position (while scrolling up the page).</p>
  
  <pre><code>$('#navigation').on('affixed.bs.affix',function(){
      $(this).height('75');
      $(this).slideDown(200);
  });
  </code></pre>
  
  <p>Does anybody have a working fiddle for a nav that works like <a href="http://www.invisionapp.com/" rel="nofollow">http://www.invisionapp.com/</a>? Thanks!</p>