Move the MPD client interface to liberty

It seems like there aren't going to be any big changes any time soon.

nncmpp.c

@@ -62,11 +62,9 @@ enum
 #define LIBERTY_WANT_POLLER
 #define LIBERTY_WANT_ASYNC
 #define LIBERTY_WANT_PROTO_HTTP
+#define LIBERTY_WANT_PROTO_MPD
 #include "liberty/liberty.c"
 
-#include <sys/un.h>
-#include "mpd.c"
-
 #include <locale.h>
 #include <termios.h>
 #ifndef TIOCGWINSZ
@@ -2395,9 +2393,6 @@ debug_tab_init (void)
 
 // --- MPD interface -----------------------------------------------------------
 
-// TODO: this entire thing has been slavishly copy-pasted from dwmstatus
-// TODO: try to move some of this code to mpd.c
-
 static void
 mpd_update_playback_state (void)
 {