title: Common legend for subplot matplotlib
body: <p>I'm creating a plot using matplotlib and it seems that I stucked with one problem.
  I draw 3 subplots and I want to get common legend for all of them</p>
  
  <pre><code>fig, (ax, ax2, ax3) = plt.subplots(3, 1, sharex=True)
  ax.plot(FRAME1['T1'],FRAME1['Num'], marker = 'o', label='1')
  ax2.plot(FRAME3['T1'],FRAME3['Num'], marker = 'o', label='2',color='r')
  ax2.plot(FRAME4['T1'],FRAME4['Num'], marker = 'o', label='3',color='turquoise')
  ax3.plot(FRAME2['T1'],FRAME2['Num'], marker = 'o', label='4',color='g')
  
  ax.set_ylim(-118, -116.5)  
  ax3.set_ylim(-136, -135)
  
  plt.legend( (ax,ax2,ax3),loc="upper left", bbox_to_anchor=[0, 1],
             ncol=2, shadow=True, title="Legend", fancybox=True)
  </code></pre>
  
  <p>I have used the legend instance but it shows legen only on the last subplot.</p>