Add hwb() + fix max for hue

Following

harthur/color-string#8
harthur/color-convert#10

+

capping must be done before convert loop for each spaces.
Otherwise it’s not coherent with how color-convert handle overflow
(modulo).

Ref #24
Aha, I see what you're saying. I think it's better than capping at 359. In that case 360 would be changed to 359 and I think that would be unexpected. http://hslpicker.com goes up to 360, as do many other color pickers I've seen.