Timer: add millis() for modbus

Timer/src/Timer.cpp

@@ -12,6 +12,7 @@ extern "C"
   void
   SysTick_Handler (void)
   {
+	systicks++;
     if (timer > 0)
       timer--;
   }
@@ -63,3 +64,7 @@ Timer::resetCounter ()
 {
   counter.store (0, std::memory_order_relaxed);
 }
+
+uint32_t millis() {
+	return systicks;
+}