draw_plot_init can't be final

[trzeci]

in file plot.h there is a method:

virtual void draw_plot_init(const Cairo::RefPtrCairo::Context &cr, const int width, const int height) final;

it should not be final.
final disables possibility to use plstream, e.g.: to change font size.

I overrode this method to change font size using pls->schr(12,0.4), but had to remove final in sources.
I think man could create many specializations of existing classes having possibility to alter plstream.
plstream is available only after draw_plot_init was invoked.