new set_stress_regions_list() filter
update fit_stress_strain() for stress regions
fix region end boundary in _plot_region_line(), _plot_fit_line()
new mark_stress_regions() plot

- move mark_strain_regions() body into new _mark_regions()
new mark_stress_regions_fits() plot

- move mark_strain_regions_fits() body into new _mark_regions_fits()
new save_stress_regions_fits() save command

- move save_strain_regions_fits() body into new _save_regions_fits()