Refactor Opus decoder

Created generic playback handler, first with Opus support. Other
decoders to follow. This is to remove duplicated code.

3DSX tested working with citra and N3DS.

Signed-off-by: Mahyar Koshkouei <deltabeard@users.noreply.github.com>

source/main.h

@@ -7,6 +7,21 @@
  * LICENSE file.
  */
 
+/* Default folder */
+#define DEFAULT_DIR		"sdmc:/"
+
+/* Maximum number of lines that can be displayed */
+#define	MAX_LIST		27
+
+enum file_types {
+	FILE_TYPE_ERROR = -1,
+	FILE_TYPE_WAV,
+	FILE_TYPE_FLAC,
+	FILE_TYPE_OGG,
+	FILE_TYPE_OPUS,
+	FILE_TYPE_MP3
+};
+
 /**
  * Get number of files in current working folder
  *