by the PlaceholderParser.
Namely, all the options with the "ratio_over" reference are now handled
correctly by the PlaceholderParser with the exception
of the "first_layer_extrusion_width", which overrides speed of extrusions
by their respective extrusion type.
Also the various extrusion widths (extrusion_width, first_layer_extrusion_width,
external_perimeter_extrusion_width etc.) produce the same numbers
as if ran through the back-end, with the assumption of not overriding
layer height by the variable layer height editing tool or layer height
modifiers.
