Adding the ping command

src/net/listen.c

@@ -162,6 +162,8 @@ handle_simple_command(struct lkt_state *srv, size_t c, struct lkt_command cmd)
 
         else if (!strcmp(cmd.name, "close"))
             err = !lkt_close_client(srv, c);
+        else if (!strcmp(cmd.name, "ping"))
+            err = 0;
 
         else if (!strcmp(cmd.name, "next"))
             err = !command_next(srv->db, &srv->win, &srv->mpd_idle_events);