Output artist and track number in Song.toString()

src/main/java/moe/nekojimi/chords/Song.java

@@ -103,10 +103,17 @@ public class Song
     @Override
     public String toString()
     {
+        String ret = "";
+        if (artist != null && !artist.isEmpty())
+            ret += artist + " - ";
+
         if (title != null && !title.isEmpty())
-            return title;
-        else
-            return "track " + number;
+            ret += title;
+
+        if (ret.isEmpty())
+            ret = "track " + number;
+
+        return "[" + number + "] " + ret;
 //            return url.toExternalForm();
     }
 }