Pie property for a Billboard.js chart
Arguments
- bb
- A - billboard- htmlwidgetobject.
- ...
- See https://naver.github.io/billboard.js/release/latest/doc/Options.html#.pie 
Examples
billboarder() %>%
  bb_piechart(data = table(mtcars$cyl)) %>% 
  bb_pie(label = list(
    ratio = 0.5, 
    format = htmlwidgets::JS("function(value) {return d3.format('$')(value);}")
  ), 
  expand = FALSE)