driver, queue: return track handle when adding an Input to the queue (#116)

src/tracks/queue.rs

@@ -165,9 +165,11 @@ impl TrackQueue {
     }
 
     /// Adds an audio source to the queue, to be played in the channel managed by `handler`.
-    pub fn add_source(&self, source: Input, handler: &mut Driver) {
-        let (audio, _) = tracks::create_player(source);
-        self.add(audio, handler);
+    pub fn add_source(&self, source: Input, handler: &mut Driver) -> TrackHandle {
+        let (track, handle) = tracks::create_player(source);
+        self.add(track, handler);
+
+        handle
     }
 
     /// Adds a [`Track`] object to the queue, to be played in the channel managed by `handler`.