Update src/main/java/br/com/digilabs/jqplot/elements/RendererOptions.java

I added fillToZero (Boolean) property.
It's usefull for BarChart with negative values.
Without a fillToZero set to true, the BarChart will render negative values in the same "Orientation" than positive values
Merge pull request #18 from vspiewak/patch-1

Update src/main/java/br/com/digilabs/jqplot/elements/RendererOptions.jav...