Removed Perl Flow::new_from_spacing bindings.
Some Fill C++11 beautification.
Fix of a support_material_1st_layer_flow, brim_flow and skirt_flow logic to use the extrusion_width if both first_layer_extrusion_width and support_material_extrusion_width are undefined.
Documented the extrusion width logic in the config tooltips, including the default values.
