Put playback in separate thread (WIP)

Selecting a file is possible whilst music is playing.
Additionally fixes #19, an issue where the Home would not appear whilst
music is playing.

TODO:
Remove printf from playback module.
Fix pause and stop.
Display errors properly using errno.

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

source/playback.h

@@ -7,7 +7,7 @@ enum file_types {
 	FILE_TYPE_MP3
 };
 
-int playFile(const char* file);
+void playFile(void* playbackInfoIn);
 
 /**
  * Obtains file type.