title: How to plot over visible x range in Bokeh
body: <p>I'm trying to plot a function over the visible x range in the view/figure.<br>
  For example, if the plot starts with X going from -4 to 4, it should plot the function from -4 to 4.<br>
  Now, if I zoom out to -8 to 8, it should plot from -8 to 8.<br>
  The same of course applies to moving on the axis i.e. if I move to -12 to 4, it should plot from -12 to 4.</p>
  
  <p>How can I achieve this?</p>