plot_conv: Clarify on PLOTTYPE possible values.
plot_conv plot_by_type(): Simplify flow by returning ASAP (and transferring plot return value)
pplot _legend() -> legend(), move the call to plot_conv's fig_by_type()
pplot legend(): Allow usage on a Figure object too
pplot fval_by_budget(): Move groupby from legend to ylabel
pplot, plot_conv: Add support for fig_overview() combining four views of the function
_fval_label(): Regression -> Regr., problems with tightmode otherwise
pplot legend(): Cramped layout, fix fontsize in whole-figure legends
plot_conv: Support PDF output
plot_conv: Use the tight layout to maximize actual plots