No support for other color spaces

[LoganDark]

It would be cool if I could do WCG (Wide Color Gamut) stuff with this crate. This would take a lot of care to do correctly though. Also see #14

[i509VCB]

On Wayland this could be even more complicated since there are many wl_shm formats (https://wayland.app/protocols/wayland#wl_shm:enum:format).

Most of the formats are somewhat unnecessary but several could be useful (Bgra8888 [reverse endian of Argb8888], Abgr8888, Rgba8888, Argb2101010, etc).

[madsmtm]

Actually, what even is the color space we do support? sRGB? Or just some platforms-specific value?