Allow option to show as percentage of parent?

[Shians]

I would like to suggest a percentMode options that has options c("total", "parent"). Under "total" the percentage will be as it currently is, but under "parent" it should show the percentage relative to the parent.

I've only made simple use of this package, but as far as I can tell the structure is fully nested, so this should be sensible. From what I can tell of the code the percentages are generated on mouse-over here. But if this percentage can't change then it probably makes sense to pre-compute this and just store it in the data element to be pulled out using d.percentage.