title: matplotlib: left yaxis and right yaxis to have different units
body: <p>I'm plotting curves in Kelvin.
  I would like to have the left yaxis to show units in Kelvin and the right yaxis to show them in Celsius, and both rounded to the closest integer (so the ticks are not aligned, as TempK=TempC+273.15)</p>
  
  <pre><code>fig=plt.figure
  figure=fig.add_subplot(111)
  figure.plot(xpos, tos, color='blue')
  </code></pre>
  
  <p>I should not use <code>twinx()</code> as it allows superimposing curves with two different scales, which is not my case (only the right axis has to be changed, not the curves).</p>