Add Vorbis decoder

Additionally implemented better handling of the playback stopping
procedure.

Signed-off-by: Mahyar Koshkouei <mk@deltabeard.com>

source/vorbis.h

@@ -0,0 +1,21 @@
+#include <tremor/ivorbiscodec.h>
+#include <tremor/ivorbisfile.h>
+#include "playback.h"
+
+void setVorbis(struct decoder_fn* decoder);
+
+int initVorbis(const char* file);
+
+uint32_t rateVorbis(void);
+
+uint8_t channelVorbis(void);
+
+uint64_t decodeVorbis(void* buffer);
+
+void exitVorbis(void);
+
+int playVorbis(const char* in);
+
+uint64_t fillVorbisBuffer(char* bufferOut);
+
+int isVorbis(const char* in);