diretory: moved code to directory_save.c, directory_print.c

Remove clutter from directory.c.  Everything which saves or loads
to/from the hard disk goes to directory_save.c, and code which sends
directory information to the client is moved into directory_print.c.

src/database.c

@@ -19,6 +19,7 @@
 
 #include "database.h"
 #include "directory.h"
+#include "directory_save.h"
 #include "song.h"
 #include "conf.h"
 #include "log.h"