pub struct SoundSys;
impl<'a> System<'a> for SoundSys {
    type SystemData = (
        Fetch<'a, AssetStorage>,
        WriteStorage<'a, SoundComp>,
    );

    fn run(&mut self, data: Self::SystemData) {
        let (assets, mut sound_comp) = data;

        for s in (&mut sound_comp).join() {
            for sound_to_play in &s.to_play {
                s.sounds[&sound_to_play].play().unwrap();
            }

            s.to_play = Vec::new();
        }
    }
}