Lift linearity restriction for Rgb and Luma and update docs

[Ogeon]

This removes the requirement that Rgb and Luma colors have to be linear for arithmetic operators and a few other traits to be available. There are many cases where non-linear colors are fine (or even required) and hard blocking them ended up being a bit too harsh.

The crate root documentation is also updated to hopefully be a bit more usage oriented and give more useful examples up-front.

[github-actions]

Benchmark for 9a83392

Click to view benchmark

Test	Base	PR	%
Cie family/lab to lch	2.2±0.01µs	2.2±0.04µs	0.00%
Cie family/lab to xyz	547.8±4.19ns	550.3±5.40ns	+0.46%
Cie family/lch to lab	1696.8±11.99ns	1704.3±25.26ns	+0.44%
Cie family/linsrgb to xyz	3.1±0.02µs	3.1±0.03µs	0.00%
Cie family/linsrgb to xyz - wide::f32x8	543.6±3.86ns	557.4±2.96ns	+2.54%
Cie family/xyz to lab	15.1±0.08µs	15.2±0.17µs	+0.66%
Cie family/xyz to yxy	470.2±3.05ns	469.3±3.12ns	-0.19%
Cie family/yxy to xyz	378.2±2.21ns	378.3±2.83ns	+0.03%
Matrix functions/matrix_inverse	8.2±0.04ns	8.3±0.16ns	+1.22%
Matrix functions/multiply_3x3	7.5±0.04ns	7.5±0.06ns	0.00%
Matrix functions/multiply_rgb_to_xyz	4.6±0.03ns	4.6±0.21ns	0.00%
Matrix functions/multiply_xyz	4.6±0.04ns	4.6±0.03ns	0.00%
Matrix functions/multiply_xyz_to_rgb	4.6±0.03ns	4.6±0.03ns	0.00%
Matrix functions/rgb_to_xyz_matrix	21.5±0.17ns	21.5±0.10ns	0.00%
Rgb family/hsl to hsv	460.7±3.20ns	461.0±4.73ns	+0.07%
Rgb family/hsl to linear hsl	9.4±0.05µs	9.1±0.06µs	-3.19%
Rgb family/hsl to rgb	1457.1±9.42ns	1422.8±12.01ns	-2.35%
Rgb family/hsv to hsl	606.4±9.61ns	606.8±9.82ns	+0.07%
Rgb family/hsv to hwb	162.3±1.46ns	159.9±1.09ns	-1.48%
Rgb family/hsv to linear hsv	8.8±0.07µs	8.7±0.05µs	-1.14%
Rgb family/hsv to rgb	1350.0±10.43ns	1326.6±8.36ns	-1.73%
Rgb family/hwb to hsv	334.2±3.87ns	333.2±3.78ns	-0.30%
Rgb family/hwb to linear hwb	9.1±0.05µs	9.2±0.06µs	+1.10%
Rgb family/linear hsl to hsl	7.6±0.04µs	7.7±0.07µs	+1.32%
Rgb family/linear hsv to hsv	7.2±0.05µs	7.2±0.06µs	0.00%
Rgb family/linear hwb to hwb	7.7±0.07µs	7.7±0.04µs	0.00%
Rgb family/linsrgb to rgb	3.9±0.03µs	3.9±0.03µs	0.00%
Rgb family/linsrgb to rgb - wide::f32x8	5.3±0.03µs	5.3±0.04µs	0.00%
Rgb family/linsrgb_f32 to rgb_u8	654.4±24.03ns	650.4±4.02ns	-0.61%
Rgb family/linsrgb_f64 to rgb_u8	835.2±4.63ns	839.8±5.50ns	+0.55%
Rgb family/rgb to hsl	568.7±2.63ns	572.5±19.95ns	+0.67%
Rgb family/rgb to hsl - wide::f32x8	353.9±1.91ns	355.0±2.57ns	+0.31%
Rgb family/rgb to hsv	362.3±3.56ns	357.5±7.09ns	-1.32%
Rgb family/rgb to hsv - wide::f32x8	315.7±2.13ns	315.9±1.64ns	+0.06%
Rgb family/rgb to linsrgb	5.3±0.05µs	5.4±0.06µs	+1.89%
Rgb family/rgb to linsrgb - wide::f32x8	4.0±0.04µs	4.0±0.04µs	0.00%
Rgb family/rgb_u8 to linsrgb_f32	235.2±3.67ns	235.5±3.58ns	+0.13%
Rgb family/rgb_u8 to linsrgb_f64	237.0±6.89ns	236.3±1.43ns	-0.30%
Rgb family/xyz to linsrgb	5.7±0.13µs	5.9±0.04µs	+3.51%
Rgb family/xyz to linsrgb - wide::f32x8	892.0±8.05ns	892.4±5.90ns	+0.04%

[Ogeon]

bors r+

[bors]

Build succeeded:

• ci