If I'm going to use this as a means of generating bitmap icons at
large sizes, I want it to support all the same modes as the existing
bitmap script. So this adds a mode to the SVG generator that produces
the same black and white colour scheme as the existing monochrome
bitmap icons.
(Plus, who knows, the black and white SVGs might come in useful for
other purposes. Printing as a logo on black-and-white printers springs
to mind.)
The existing monochrome icons aren't greyscale: all colours are
literally either black or white, except for the cardboard box in the
installer icon, which is halftoned. Here I've rendered that box as
mid-grey. When I convert the rendered SVG output to an actual
1-bit (plus alpha) image, I'll have to redo that halftoning.
