fix: ``rgb2hsl`` would produce invalid hsl triplet when red, blue, green component would be all very close to ``1.0``. (fixes #30)
fix: ``rgb2hsl`` would produce invalid hsl triplet when red, blue, green component would be all very close to ``1.0``. (fixes #30)

Typically, saturation would shoot out of range 0.0..1.0. That could then
lead to exceptions being casts afterwards when trying to reconvert this
HSL triplet to RGB values.

vaab/colour,vaab/colour