Start the loop.

    :param `leds`: Which LEDs to light up upon switch press.
    :type `leds`: sequence of LED objects

def run_loop(leds=all_leds):
    """
    Start the loop.

    :param `leds`: Which LEDs to light up upon switch press.
    :type `leds`: sequence of LED objects
    """
    print('Loop started.\nPress Ctrl+C to break out of the loop.')
    while 1:
        try:
            if switch():
                [led.on() for led in leds]
            else:
                [led.off() for led in leds]
        except OSError: # VCPInterrupt # Ctrl+C in interpreter mode.
            break