Add SID support (libsidplay required)

source/sid.h

@@ -0,0 +1,44 @@
+#include <stdint.h>
+#include "playback.h"
+
+/**
+ * Set decoder parameters for SID.
+ *
+ * \param	decoder Structure to store parameters.
+ */
+void setSid(struct decoder_fn* decoder);
+
+/**
+ * Initialise SID playback.
+ *
+ * \param	file	Location of SID file to play.
+ * \return			0 on success, else failure.
+ */
+int initSid(const char* file);
+
+/**
+ * Get sampling rate of SID file.
+ *
+ * \return	Sampling rate.
+ */
+uint32_t rateSid(void);
+
+/**
+ * Get number of channels of SID file.
+ *
+ * \return	Number of channels for opened file.
+ */
+uint8_t channelSid(void);
+
+/**
+ * Read part of open SID file.
+ *
+ * \param buffer	Output.
+ * \return			Samples read for each channel.
+ */
+uint64_t readSid(void* buffer);
+
+/**
+ * Free SID file.
+ */
+void exitSid(void);