title: Create a two line legend in a bokeh plot
body: <p>I'm trying to create a Bokeh chart with alot of individual lines on it, 14 to be exact (not my idea, was told to do it this way). Problem is that the requested formatting has the legend horizontal along the bottom of the chart and it's to long to fit so I need it to be two lines and I can't seem to find any indication on how to do this. Hoping someone has had to tackle this before.</p>
  
  <p>Current code with a single line legend. </p>
  
  <pre><code>#graph data to chart
  r0  = p1.line(data['Time'], data['Signal 1'], line_color="MediumBlue")
  r1  = p1.line(data['Time'], data['Signal 2'], line_color="MidnightBlue")
  r2  = p1.line(data['Time'], data['Signal 3'], line_color="red", y_range_name="Temp")
  r3  = p1.line(data['Time'], data['Signal 4']*10, line_color="gray", y_range_name="Temp")
  r4  = p1.line(data['Time'], data['Signal 5']*3.281, line_color="gold")
  r5  = p1.line(data['Time'], data['Signal 6'], line_color="brown", y_range_name="Temp")
  r6  = p1.line(data['Time'], data['Signal 7'], line_color="tomato", y_range_name="Temp")
  r7  = p1.line(data['Time'], data['Signal 8'], line_color="blue", line_dash="4 4", y_range_name="Temp")
  r8  = p1.line(data['Time'], data['Signal 9'], line_color="cyan", y_range_name="Temp")
  r9  = p1.line(data['Time'], data['Signal 10']*57.3, line_color="plum", y_range_name="Temp")
  r10 = p1.line(data['Time'], data['Signal 11']*1.94, line_color="green", y_range_name="Temp")
  
  #create html file
  output_file("Engine_Disp_Test.html", title="Engine Disp Test")
  
  #Configure Legend
  legend=Legend(items=[
                       ("Signal 1" , [r0]),
                   ("Signal 2" , [r1]),
                   ("Signal 3" , [r2]),
                   ("Signal 4" , [r3]),
                   ("Signal 5", [r4]),
                   ("Signal 6", [r5]),
                   ("Signal 7", [r6]),
                   ("Signal 8", [r7]),
                   ("Signal 9", [r8]),
                   ("Signal 10", [r9]),
                   ("Signal 11", [r10])
                   ], location=(70,-10), orientation="horizontal")
  </code></pre>