title: CGAffineTransform revert the rotating direction
body: <p>I'm rotating 360º a UIButton using this code:</p>
  
  <pre><code>self.btn.transform = CGAffineTransform(rotationAngle: (180.0 * CGFloat(M_PI)) / 180.0)
      self.btn.transform = CGAffineTransform(rotationAngle: (0.0 * CGFloat(M_PI)) / 180.0)
  </code></pre>
  
  <p>The problem is that it rotates from left to right and i want to invert the direction.
  I have tried using -M_PI, or -180 and other combinations, but without success.
  What am i doing wrong?</p>