libsaria: Move include/audio.h to the audio directory

The audio class can easily be defined in a file located in the audio/
directory.  This frees up the audio.h name for a UI-facing include file.

libsaria/audio.cpp

@@ -1,7 +1,8 @@
 
 #include <libsaria/libsaria.h>
 #include <libsaria/callback.h>
-#include <libsaria/audio.h>
+
+#include "audio/audio.h"
 
 static Audio audio;
 

libsaria/audio/audio.cpp

@@ -1,6 +1,6 @@
 
-#include <libsaria/audio.h>
 #include <libsaria/print.h>
+#include "audio.h"
 
 static bool initialized = false;
 static void init_gstreamer(int argc, char **argv)

libsaria/audio/controls.cpp

@@ -1,6 +1,6 @@
 
-#include <libsaria/audio.h>
 #include <libsaria/print.h>
+#include "audio.h"
 
 bool Audio::change_state(GstState new_state)
 {

libsaria/audio/progress.cpp

@@ -1,5 +1,5 @@
 
-#include <libsaria/audio.h>
+#include "audio.h"
 
 bool Audio::get_duration(gint64 &duration)
 {

libsaria/audio/volume.cpp

@@ -1,5 +1,5 @@
 
-#include <libsaria/audio.h>
+#include "audio.h"
 
 void Audio::set_volume(double volume)
 {