iOS / PNChart

Add options for chart legend font style.

Fix #177

Conflicts:
	PNChart/PNGenericChart.h
	PNChartDemo/PCChartViewController.m

Interactive Pie

Add PNLineChart with setYLabels.

Avoid labels on Y axis duplicate

…xis (_yLabelSum) depends on the number of different Y values, avoiding the  duplicate labels on Y axis.
Also modify getYValueMax and setYValues methods to ensure the max value of Y axis (_yValueMax) and the number of labels on Y axis (_yLabelSum) are even to avoid when the Y labels hasn't decimal values (default value for _yLabelFormatter) the axis label position not match with the value

This reverts commit c330cf08.

This reverts commit e200b9ba, reversing
changes made to 4da58d16.

Update readme with example for legend

Legend 

getAxisMinMax - Determine these values automagically

Update PNLineChart.m

PieChart divides equally when all value of data items are 0

Show actual percentage in label

The label was showing stuff like 6000% which is not relevant if it says the % or maybe %%%.

Anyway I feel this way it is better for a default use?

I found it very useful to have this... especially for testing if not for production purposes.

Will need in the .h:
- (NSArray*) getAxisMinMax:(NSArray*)xValues;