@Override
    public PieChartData getPieChartData() {
        return data;
    }
PieChart is a little different than others charts. It doesn't have axes. It doesn't support viewport so changing
viewport wont work. Instead it support "Circle Oval". Pinch-to-Zoom and double tap zoom wont work either. Instead of
scroll there is chart rotation if isChartRotationEnabled is set to true. PieChart looks the best when it has the same
width and height, drawing chart on rectangle with proportions other than 1:1 will left some empty spaces.

@author Leszek Wach
hellocharts-library/src/lecho/lib/hellocharts/view/PieChartView.java