Fix PieChart values overlap

[hannesa2]

close #106

[hannesa2]

I grab the changes from https://github.com/huzipiaopiao/MPAndroidChartFix but it looks ugly

[hannesa2]

Screenshot differs:9 10

PieTest_piePolyline.png

PieTest_piePolyline1-10.png

PieTest_piePolyline1-20.png

PieTest_piePolyline1-30.png

PieTest_piePolyline1-40.png

PieTest_piePolyline1-50.png

PieTest_piePolyline2-100.png

PieTest_piePolyline2-150.png

PieTest_piePolyline2-200.png

PieTest_piePolyline2-50.png