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/main.h

@@ -13,6 +13,8 @@
 /* Maximum number of lines that can be displayed */
 #define	MAX_LIST		27
 
+static int changeFile(const char* ep_file, Thread* thread, struct playback_t* playbackInfo);
+
 /**
  * Get number of files in current working folder
  *