Code to place the chosen __data_empty_label in the center of the main chart when 0 targets supplied. Takes into account sub chart being active.
Styling has been moved to c3.css

Update c3.js, getInterporate being used to fill interpolate value. ...porate vs ...polate

Shouldn't getInterporate be getInterpolate to match what it is being used for?

Added chart_arc_gauge.html as a sample/demo of functionality. Added c3.update function to update configurations in the demo.

Added chart_arc_gauge.html as a sample/demo of functionality. Added c3.update function to update configurations in the demo.