libsaria: Added a get_progress() function to the audio namespace

This function is used to access how far into the song the current audio
position is.  The value is returned as a percentage of the total length
for easy use by the UI.

include/libsaria/audio.h

@@ -20,6 +20,7 @@ namespace libsaria
 		/* Position related functions */
 		bool seek(int);
 		bool seek_to(double);
+		int get_progress();
 
 		/* Volume functions */
 		double get_volume();

libsaria/audio/progress.cpp

@@ -57,4 +57,15 @@ namespace libsaria
 		return ret;
 	}
 
+	int audio::get_progress()
+	{
+		gint64 progress;
+		gint64 duration;
+		if (!get_position(progress))
+			return 0;
+		if (!get_duration(duration))
+			return 0;
+		return (progress * 100) / duration;
+	}
+
 };