Violin plots?
Besides boxplots, another way to look at the distribution of data is by violin plots:

http://nbviewer.ipython.org/gist/olgabot/7902901

I'd like to add this to pandas. Is there interest in these plots? It currently depends on my `prettyplotlib` but that can be removed. My concern is that it depends on `scipy.stats.gaussian_kde` - is that fine?
