title: How to calculate first NSDate of current week?
body: <p>i.e.:</p>
  
  <pre><code>  NSDate *firstDayOfWeek = [[NSDate date] firstDayOfWeek];
  </code></pre>
  
  <p>for example, today is Aug 19, I'd want to get a <code>NSDate</code> of <code>2010-08-15 12:00am</code> from above line of code. Thanks!</p>