public Line setFormatter(LineChartValueFormatter formatter) {
        if (null != formatter) {
            this.formatter = formatter;
        }
        return this;
    }
Set path effect for this line, note: it will slow down drawing, try to not use complicated effects,
DashPathEffect should be safe choice.

@param pathEffect
hellocharts-library/src/lecho/lib/hellocharts/model/Line.java