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
I'll push that changes but I deeply think we should just drop "capping", and handle the angle value like it can be: modulo 360. I mean that 720deg is a valid hue for hsl & friends.