Add Color::srgb_u32

[amytimed]

Objective

Allows using a color value like 0xffffff.

Instead of doing this:

let r = ((delta.background_color >> 16) & 0xff) as f32 / 255.;
let g = ((delta.background_color >> 8) & 0xff) as f32 / 255.;
let b = (delta.background_color & 0xff) as f32 / 255.;

let color = Color::srgb(r, g, b);

This PR allows doing this:

let color = Color::srgb_u32(delta.background_color);

Solution

New method srgb_u32, similar to srgb_u8 but all in one value.

[alice-i-cecile]

This should call an equivalent public method on Srgba :)

[alice-i-cecile]

I still want this comment resolved :)

[mnmaita]

@amytimed thanks for such an useful contribution! Would you be able to address the comments? I think this PR is an easy win if you include the requested additions.