lots of changes

- GUI: ability to load files
- GUI: arrow key navigation
- fix sample volumes

src/engine/platform/sms.cpp

@@ -183,3 +183,10 @@ int DivPlatformSMS::init(DivEngine* p, int channels, int sugRate, bool pal) {
   reset();
   return 4;
 }
+
+void DivPlatformSMS::quit() {
+  delete sn;
+}
+
+DivPlatformSMS::~DivPlatformSMS() {
+}