Simple sorting of colors and background-colors.

Sort colors by first comparing Hue, then Saturation, then Lightness
and finally the Alpha component.  The result is that similar colors
get grouped together - e.g. the gray tones are all clustered together,
the reds together with other reds, greens with other greens etc.

Added dependency on csscolorparser to parse CSS color strings into
RGB arrays.

Added dependency on colr to convert from RGB to HSL.