title: multi_line hover in bokeh
body: <p>As in this question: </p>
  
  <p><a href="https://stackoverflow.com/questions/32975709/bokeh-multi-line-and-hovertool">Bokeh multi_line and HoverTool</a></p>
  
  <p>I found that hovertool is not implemented for multi_line plots which is a bit of a setback. This is mentioned under 'warnings' here: <a href="http://docs.bokeh.org/en/0.11.0/docs/reference/models/tools.html#bokeh.models.tools.HoverTool" rel="nofollow noreferrer">http://docs.bokeh.org/en/0.11.0/docs/reference/models/tools.html#bokeh.models.tools.HoverTool</a></p>
  
  <p>Is there any work arounds for this?
  Also, If I were to implement this feature, what would be a good place to start and is there anything specific to be aware of?
  Also, is this feature in the current Bokeh roadmap?</p>