iOS / PNChart

I added this property because showing all labels, when there are a lot of small items in the dataset, is quite confusing.

Example:
piechart.labelPercentageCutoff = 0.05
hide all labels with value less than 5% (I use this most of the times).

Merge from origin

Add prefix/suffix public property for y label values

Make countingLabel show updated percent instead of absolute value

Too ugly that I can not stand with.

Add the new feature that supports show the negative numbers

Line chart ylabel formatter block

Optimize Negative show

Klauslanza line chart ylabel formatter

Update

optimize gradient show

- Fix for issue: https://github.com/kevinzhow/PNChart/issues/198

Added the new feature support custom yLabels

…ty and did not show any graphics.