wallpaper crate docs

This Rust library gets and sets the desktop wallpaper/background.

The supported desktops are: * Windows * macOS * GNOME * KDE * Cinnamon * Unity * Budgie * XFCE * LXDE * MATE * Deepin * i3 (set only, requires feh)

Example

```rust extern crate wallpaper;

fn main() { println!("{:?}", wallpaper::get().unwrap()); wallpaper::setfrompath("/usr/share/backgrounds/gnome/adwaita-day.png").unwrap(); wallpaper::set_mode(wallpaper::Mode::Crop).unwrap(); println!("{:?}", wallpaper::get().unwrap()); } ```