Set multiple pins high or low at once.  Pins should be a dict of pin
        name to pin value (HIGH/True for 1, LOW/False for 0).  All provided pins
        will be set to the given values.

def _output_pins(self, pins):
        """Set multiple pins high or low at once.  Pins should be a dict of pin
        name to pin value (HIGH/True for 1, LOW/False for 0).  All provided pins
        will be set to the given values.
        """
        [self._validate_channel(pin) for pin in pins.keys()]
        # Set each changed pin's bit.
        for pin, value in iter(pins.items()):
            if value:
                self.gpio[int(pin/8)] |= 1 << (int(pin%8))
            else:
                self.gpio[int(pin/8)] &= ~(1 << (int(pin%8)))
        # Write GPIO state.
        self._write_gpio()