improve the timer and add a stopwatch subcmd (wip)

include/subcmds.h

@@ -6,6 +6,7 @@
  */
 
 void timer_subcmd(void *, int argc, char *argv[]);
+void stopwatch_subcmd(void *, int argc, char *argv[]);
 void subcmds_dev(void *, int argc, char *argv[]);
 void motd_subcmd(void *, int argc, char *argv[]);
 void subcmds_subcmd(void *, int argc, char *argv[]);