title: How do i combine multiple bar charts in bokeh?
body: <p>I want to plot two bar charts on the same figure.</p>
  
  <p>One will have only positive values, one will have only negative values.</p>
  
  <p>I want the positive bars in green (above the x-axis) and the negative bars in red (below the x-axis)</p>
  
  <p><strong>Questions:</strong></p>
  
  <p><strong>1. Is it possible to do this with the existing highlevel Bar method in the bokeh.charts interface?</strong></p>
  
  <p><strong>2. If not, how can I create a bar chart using the lower level bokeh.plotting interface? (rather than the higher level bokeh.charts interface)</strong></p>