+ Buttons Driver done
   * can read up to 2 values
     first value is currently active
     buttons, second value is last
     active buttons
 - LEDs driver need to be fixed with
   I/O ports change, change flat cable
   for buttons and LEDs

 - Should we have interrupt function
   registered in buttons_driver?
     * Now button status is only updated
       If user presses a button when read
       function for driver is called.