output: move functions into the AudioOutput struct

src/output/plugins/RoarOutputPlugin.cxx

@@ -58,7 +58,7 @@ public:
 	}
 
 	bool Initialize(const config_param &param, Error &error) {
-		return ao_base_init(&base, param, error);
+		return base.Configure(param, error);
 	}
 
 	void Configure(const config_param &param);