title: Sort numpy 2d array by multiple columns
body: <p>I have a 2D numpy array that looks like this</p>
  <pre><code>array([[5, 0],
         [3, 1],
         [7, 0],
         [2, 1]])
  </code></pre>
  <p>I'd like to (sub) sort by each column (say right to left) to get this:</p>
  <pre><code>array([[5, 0],
         [7, 0],
         [2, 1],
         [3, 1]])
  </code></pre>
  <p>How can I do that in numpy?</p>