title: Format numbers as billions / millions / thousands, smartly
body: <p>Any recipes out there for a "smart" number formatting formula that's "scale-aware," a la Rails ActionView's <a href="http://api.rubyonrails.org/classes/ActionView/Helpers/DateHelper.html#method-i-distance_of_time_in_words" rel="nofollow">distance_of_time_in_words</a> method?</p>
  
  <p>I would expect to enter a number like: 1,816,724 and see <strong>1.8M</strong> (or enter 2,394 and see <strong>2.4K</strong>).</p>