Using dbus-rs (v0.6) to get value of new DBus property from the signal message

gistfile1.rs

```
extern crate dbus;
use dbus::{BusType, Connection, SignalArgs};
use dbus::stdintf::org_freedesktop_dbus::PropertiesPropertiesChanged;

fn main() {
    let c = Connection::get_private(BusType::Session).unwrap();
    let matched_signal = PropertiesPropertiesChanged::match_str(Some(&"localhost.statusbar.DBus".into()), Some(&"/localhost/statusbar/DBus/SoundDevice".into()));
    c.add_match(&matched_signal).unwrap();
    loop {
        for msg in c.incoming(1000) {
            if let Some(signal) = PropertiesPropertiesChanged::from_message(&msg) {
                let value = signal.changed_properties.get("Status").unwrap();
                let status = value.0.as_str().unwrap();
                println!("Status changed to: {}", &status);
            }
        }
    }
}
```