title: CorePlot zoom axes independently with multi-touch
body: <p>I have a iPhone app with a CorePlot graph.  I would like the user to be able to zoom in and out of the graph similar to the default functionality except for one thing:</p>
  
  <ul>
  <li>When the user pinches horizontally -> zoom the x-axis.</li>
  <li>Vertically -> zoom the y-axis.</li>
  <li>Diagonally -> zoom both axes.</li>
  </ul>
  
  <p>How can I implement this functionality?  Any suggestions would be appreciated.</p>