title: Bokeh image section
body: <p>I am using bokehjs from python in order to display 2d gl array as images or heat map.
  Generally, in different tools i know, In order to explore the data there is a popular data analysis feature of "section" that you mark on the image and see a 1d graph of the image gl.
  Does it exist on bokeh?
  If not, what is the best choice of creating it?</p>