title: Ruby Date Subtraction (e.g. 90 days Ago)
body: <p>I've been a bit spoiled by the joda-time API of:</p>
  
  <pre><code>DateTime now = new DateTime();
  DateTime ninetyDaysAgo = now.minusDays(90);
  </code></pre>
  
  <p>I'm trying to do a similar thing in Ruby, but I'm </p>
  
  <pre><code>now = Time.now
  ninetyDaysAgo = now - (90*24)
  </code></pre>
  
  <p>However, the math is off here (I'm really working with dates at midnight).</p>
  
  <p>Is there friendly API for date subtraction?</p>