Feature: Adding boxen plot?

[tyamaguchi-ucla]

We might want to consider adding "boxen plot" (enhanced box plot or letter-value plot) as a new function since we handle numerous large datasets. It might not require too much work as the function seems to be similar to a boxplot with additional breakdown points. Any thoughts? @dan-knight

how-boxen-plot-is-different-from-box-plot

Original paper - Letter-value plots: Boxplots for large data
https://vita.had.co.nz/papers/letter-value-plot.html

[pboutros]

I like this in general, but would like to see the upset function we have polished off & added as a higher priority