title: Convert duration to hours:minutes:seconds (or similar) in Rails 3 or Ruby
body: <p>I have a feeling there is a simple/built-in way to do this but I can't find it.</p>
  
  <p>I have a duration (in seconds) in an integer and I want to display it in a friendly format.</p>
  
  <p>e.g. 3600 would be displayed as "01:00:00" or "1 hour" or something.</p>
  
  <p>I can do it with <code>time_ago_in_words(Time.zone.now+3600)</code> but that feels like a bit of a hack, there is no reason to add/subtract from the current time just to format this value.  Is there a <code>duration_in_words()</code> or something?</p>
  
  <p>Thanks</p>