cherry pick from amster: improvement: now call millis() one time over an update 40c7c1e89a9d98175d0ace74450700d7c844f361
maintain void update(void) for backward compatibility
now time can be proportionated by the user when he calls update over a Timer object. It maintains backward compatibility
Merge pull request #11 from niesteszeck/v2.1

cherry pick from master: improvement: now call millis() one time over an...