Fix glitched HLS conversion

Fixes a bug inherited from XTerm where the algorithm discards fractions from the hue while still needed. Additionally, XTerm converts to an RGB color space with components 0..100 due to architectural limitations, but st-sx does not have these, so I've changed it to convert to 0..255 directly for more accurate results. You can check `img2sixel -t hls some_image.png` before & after the patch to see the difference.