Added mouseover and mouseout support for Polar Area charts.

I followed the logic of jhdavids8 modifications and adapted it to Polar Area charts (code is a bit lengthier because it is more complicated to check if the mouse is inside a polar area than hovering over a point. For more information check this [SO question](http://stackoverflow.com/questions/13652518/efficiently-find-points-inside-a-circle-sector))