title: Zoomable Treemap in Bokeh
body: <p>I was wondering if anyone had any links to work for a zoomable treemap in Bokeh.  Similar to the Mike Bostock example: <a href="https://bost.ocks.org/mike/treemap/" rel="noreferrer">https://bost.ocks.org/mike/treemap/</a>  </p>
  
  <p>In particular:  there doesn't seem to be (as yet) a treemap layout in Bokeh, perhaps this would be the first place to start?  Then I would assume that some form of animation would need to be done to flow from one tree hierarchy to the next.</p>