def get_bit_mask(bit_num):
return <NUM_LIT:1> << (bit_num)<EOL>
Returns as bit mask with bit_num set.

    :param bit_num: The bit number.
    :type bit_num: int
    :returns: int -- the bit mask
    :raises: RangeError

    >>> bin(pifacecommon.core.get_bit_mask(0))
    1
    >>> pifacecommon.core.get_bit_mask(1)
    2
    >>> bin(pifacecommon.core.get_bit_mask(3))
    '0b1000'