public ColumnChartData setFillRatio(float fillRatio) {
        if (fillRatio < 0) {
            fillRatio = 0;
        }
        if (fillRatio > 1) {
            fillRatio = 1;
        }
        this.fillRatio = fillRatio;
        return this;
    }
Set fill ration for columns, value from 0 to 1, 1 means that there will be almost no free space between columns,
0 means that columns will have minimum width(2px).

@param fillRatio
@return
hellocharts-library/src/lecho/lib/hellocharts/model/ColumnChartData.java