absolute coordinates add 10~20% to size, consider optimizing path strings

[anthrotype]

After I rebuild our test color-fonts using latest nanoemoji and picosvg in googlefonts/color-fonts#11, I noticed that the OT-SVG fonts that embed SVGs converted through picosvg (--color_format=picosvg/picosvgz) are now between 10 to 20 % bigger. I think this is a result of picosvg now always converting coordinates to absolute, for all paths, not just those that need to be simplified for various reasons (e.g. processing with other tools like skia-pathops).

Maybe as an optional optimization picosvg could make path d strings more compact by using relative coordinates, as well as reducing whitespace between path commands to the mimimum, and similar other size optimizations.

[rsheeter]

@EsoHasInsomnia was asking about using picosvg for shrinking svgs which is somewhat related. A shrink mode is worth at least considering.