title: add title to collection of pandas hist plots
body: <p>I'm looking for advice on how to show a title at the top of a collection of histogram plots that have been generated by a pandas df.hist() command. For instance, in the histogram figure block generated by the code below I'd like to place a general title (e.g. 'My collection of histogram plots') at the top of the figure:</p>
  
  <pre><code>data = DataFrame(np.random.randn(500).reshape(100,5), columns=list('abcde'))
  axes = data.hist(sharey=True, sharex=True)
  </code></pre>
  
  <p>I've tried using the <em>title</em> keyword in the hist command (i.e. title='My collection of histogram plots'), but that didn't work.</p>
  
  <p>The following code <em>does</em> work (in an ipython notebook) by adding text to one of the axes, but is a bit of a kludge.</p>
  
  <pre><code>axes[0,1].text(0.5, 1.4,'My collection of histogram plots', horizontalalignment='center',
                 verticalalignment='center', transform=axes[0,1].transAxes)
  </code></pre>
  
  <p>Is there a better way?</p>