patch 8.1.1502: cannot play any sound

Problem:    Cannot play any sound.
Solution:   Use libcanberra if available.  Add sound functions.
diff --git a/src/proto/sound.pro b/src/proto/sound.pro
new file mode 100644
index 0000000..43e4727
--- /dev/null
+++ b/src/proto/sound.pro
@@ -0,0 +1,7 @@
+/* sound.c */
+void f_sound_playevent(typval_T *argvars, typval_T *rettv);
+void f_sound_playfile(typval_T *argvars, typval_T *rettv);
+void f_sound_stop(typval_T *argvars, typval_T *rettv);
+void f_sound_stopall(typval_T *argvars, typval_T *rettv);
+void sound_free(void);
+/* vim: set ft=c : */