Cross-fade animation

[JCsplash]

@sindresorhus thanks for the great library! Not sure if this is possible but any way we could add a cross fade animation to changing wallpapers?

[sindresorhus]

It's possible, but not easy. We would have to add a NSWindow containing a copy of the existing wallpaper at the same window level as the desktop plus one, change the actual wallpaper, then fade out the window. That would create the illusion of cross-fading.

Not something I plan to work on though, but a high-quality pull request would be welcomed.