title: Double donut chart in matplotlib
body: <p>Alright matplotlib afficionados, we know how to plot a <a href="https://stackoverflow.com/questions/36296101/donut-chart-python">donut chart</a>, but what is better than a donut chart? A double-donut chart. Specifically: We have a set of elements that fall into disjoint categories and sub-categories of the first categorization. The donut chart should have slices for the categories in the outer ring and slices for the sub-categories in the inner ring, obviously aligned with the outer slices. </p>
  
  <p>Is there any library that provides this or do we need to work this out here?</p>
  
  <p><a href="https://i.stack.imgur.com/BCM0N.png" rel="noreferrer"><img src="https://i.stack.imgur.com/BCM0N.png" alt="enter image description here"></a></p>