Add support of bitfields

[insolor]

https://docs.python.org/3/library/ctypes.html#bit-fields-in-structures-and-unions
Original:

class Int(Structure):
    _fields_ = [("first_16", c_int, 16),
                ("second_16", c_int, 16)]

Concept of the implementation

class Int(AnnotatedStructure):
    first_16 = bitfield(c_int, 16)
    second_16 = bitfield(c_int, 16)