Support for KEY_PROGs

[dragonnn]

Wanted ask if you can add support for KEY_PROG1,2,3,4? I am creating an issue because I am not sure how would that work on Windows/MacOS, on Linux that is straight forward, only need to add them to the Keycode enum and too kernel_key_to_keycode For me it would be perfectly fine to have those keys only working on Linux, I am working on a program for doing some power management on my laptop and it has two nice keys dedicated to it with emit KEY_PROG1 and KEY_PROG2.

Would be fine to add those keys but mark them with #[cfg(target_os = "linux")], in this way when someone would try to use them on MacOS/Windows it would give a compiler error?

Of course is someone finds what codes are for those keys on Windows/MacOS then they could be add too, but I am even not sure if they exist on those systems.