Provide msclock() as Milliseconds timer for performance measures (#231)

- don't use clock(). It has different functionalities in Windows and Linux
- move sleep functions to util.h

client/cmdlfhitag.c

@@ -19,7 +19,6 @@
 #include "util.h"
 #include "hitag2.h"
 #include "hitagS.h"
-#include "sleep.h"
 #include "cmdmain.h"
 
 static int CmdHelp(const char *Cmd);