title: Shade 'cells' in polar plot with matplotlib
body: <p>I've got a bunch of regularly distributed points (θ = n*π/6, r=1...8), each having a value in [0, 1]. I can plot them with their values in matplotlib using</p>
  
  <pre><code>polar(thetas, rs, c=values)
  </code></pre>
  
  <p>But rather then having just a meagre little dot I'd like to shade the corresponding 'cell' (ie. everything until halfway to the adjacent points) with the colour corresponding to the point's value:</p>
  
  <p><img src="https://i.stack.imgur.com/1Xfzf.png" alt="Polar plot with shaded cells"></p>
  
  <p>(Note that here my values are just [0, .5, 1], in really they will be everything between 0 and 1. Is there any straight-forward way of realising this (or something close enough) with matplotlib? Maybe it's easier to think about it as a 2D-histogram?</p>