Plot histograms like violin plots

[sethaxen]

There should be an option for plotting histograms similarly to violin plots.
That is, with the ability to plot them vertically as well as horizontally, with an x value that indicates the group id, such that switching from violin to this function produces histograms where there were violins.

I'm not certain whether this is best implemented with a new recipe or if there's a way to tweak the histogram recipe to make this possible.