Initial MP3 refactor

Using mpg123_outblock doesn't work correctly. Also assigning variables
to different types.

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

source/mp3.h

@@ -1,3 +1,45 @@
 #include <mpg123.h>
 
+/**
+ * Set decoder parameters for MP3.
+ *
+ * \param	decoder Structure to store parameters.
+ */
+void setMp3(struct decoder_fn* decoder);
+
+/**
+ * Initialise MP3 decoder.
+ *
+ * \param	file	Location of MP3 file to play.
+ * \return			0 on success, else failure.
+ */
+int initMp3(const char* file);
+
+/**
+ * Get sampling rate of MP3 file.
+ *
+ * \return	Sampling rate.
+ */
+uint32_t rateMp3(void);
+
+/**
+ * Get number of channels of MP3 file.
+ *
+ * \return	Number of channels for opened file.
+ */
+uint8_t channelMp3(void);
+
+/**
+ * Decode part of open MP3 file.
+ *
+ * \param buffer	Decoded output.
+ * \return			Samples read for each channel.
+ */
+uint64_t decodeMp3(void* buffer);
+
+/**
+ * Free MP3 decoder.
+ */
+void exitMp3(void);
+
 int playMp3(const char* in);