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/command.c

@@ -21,6 +21,7 @@
 #include "playlist.h"
 #include "ls.h"
 #include "directory.h"
+#include "directory_print.h"
 #include "database.h"
 #include "update.h"
 #include "volume.h"