Fixed bugs that were preventing NVR and Flash files from behind saved;

A lot of clean ups from waltje;
Start of a directory structure for the code, thanks to waltje.

src/SOUND/snd_dbopl.h

@@ -0,0 +1,17 @@
+/* Copyright holders: The DOSBox Team, SA1988
+   see COPYING for more details
+*/
+#ifdef __cplusplus
+extern "C" {
+#endif
+        void opl_init(void (*timer_callback)(void *param, int timer, int64_t period), void *timer_param, int nr, int is_opl3);
+        void opl_write(int nr, uint16_t addr, uint8_t val);
+        uint8_t opl_read(int nr, uint16_t addr);
+        void opl_timer_over(int nr, int timer);
+        void opl2_update(int nr, int16_t *buffer, int samples);
+        void opl3_update(int nr, int16_t *buffer, int samples);
+
+	extern int opl3_type;
+#ifdef __cplusplus
+}
+#endif