title: How to plot a 2d array with bokeh?
body: <p>Can someone give a short/simple example of how to plot a 2D-array with bokeh? Something similar to <code>imshow()</code> in matplotlib. I did not find a good examples given in the bokeh gallery. </p>
  
  <pre><code>a = np.array([[1,2], [3, 4]])
  imshow(a)  # but with bokeh
  </code></pre>