Update NVD3 support

[clecocel]

This updates the NVD3 JS library, and allows to modify the chart.pie via the $pie function in nvd3 class. This allows to create a half-donut as demonstrated here: https://github.com/nvd3-community/nvd3/blob/gh-pages/examples/pieChart.html

a minimum working example demonstrating value is:

p5 <- nPlot(~ cyl, data = mtcars, type = 'pieChart')
p5
p5$pie(startAngle="#! function(d){return d.startAngle/2-Math.PI/2;} !#",
       endAngle="#! function(d){return d.endAngle/2-Math.PI/2;} !#")

[clecocel]

By the way, thank you very much for all the work you put into this, I just discovered the library, so I have been fiddling around with it, but it seems super powerful!