ENH: use suptitle to plot the title of a plot on faceting
ENH: use suptitle to plot the title of a plot on faceting

On faceting, the title is addded to the figure and not to individual
axis which breaks on faceting.

See https://github.com/yhat/ggplot/issues/47#issuecomment-30340126

has2k1/plotnine,has2k1/plotnine