[Feature] add support for hex8

[lukasoppermann]

Maybe by adding a new function toHex8 that outputs the hex value with transparency.

[ricokahler]

This library does support outputting to hex8 but only when the alpha value is less than one. For the sake of keeping the API stable, I'll close this one for now.

color2k/src/toHex.test.ts

Line 17 in a16e502

expect(toHex('rgba(0, 255, 0, 0.5)')).toMatchInlineSnapshot(`"#00ff0080"`);

[lukasoppermann]

Ahh, nice, maybe you could add this to the description of toHex?