To quickly convert the SVG's to PNG's, use inkscape:
$ s=64
$ inkscape -h $s -w $s -e icon-$s.png icon-48.svg
$ s=256
$ inkscape -h $s -w $s -e icon-$s.png icon-512.svgWhen adding new files here, make sure to crush them first. You can use libdot/bin/imgcrush to do so losslessly.