title: CGAffineTransform from two lines - each represented by a pair of CGPoints
body: <p>You can probably see where I am going with this - but is there any <strong>easy</strong> way to generate a CGAffineTransform from two lines - each represented by a pair of CGPoints:</p>
  
  <pre><code>A[(a1x,a1y), (a2x,a2y)],
  B[(b1x,b1y), (b2x,b2y)]
  </code></pre>
  
  <p>The resultant CGAffineTransform when applied to line A would of course produce line B. It potentially could involve a translation, scale, and rotation.</p>
  
  <p>Certainly I would hope to be able to write this myself after brushing up on some trig but I was wondering if anything is already available to do this?</p>
  
  <p><strong>Note:</strong> I am not asking you to write this for me - I just don't want to miss a Core Graphics trick!</p>