Function spawn 

pub fn spawn<Args, Arg, Env, Key, Value>(
    program: &str,
    args: Args,
    env: Option<Env>,
) -> Result<()>
where
    Args: IntoIterator<Item = Arg>,
    Arg: AsRef<OsStr>,
    Env: IntoIterator<Item = (Key, Value)>,
    Key: AsRef<OsStr>,
    Value: AsRef<OsStr>,