rfc3339.FixedOffset_type is not copyable

[Nipsuli]

Cannot use copy.deepcopy for datetime objects created with udatetime as deepcopy fails for rfc3339.FixedOffset_type. Example:

>>> import udatetime
>>> import datetime
>>> import pytz
>>> from copy import deepcopy
>>> dtu = udatetime.now()
>>> # deepcopy fails
... deepcopy(dtu)
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
  File "/usr/local/lib/python3.7/copy.py", line 180, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/usr/local/lib/python3.7/copy.py", line 274, in _reconstruct
    y = func(*args)
  File "/usr/local/lib/python3.7/copy.py", line 273, in <genexpr>
    args = (deepcopy(arg, memo) for arg in args)
  File "/usr/local/lib/python3.7/copy.py", line 180, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/usr/local/lib/python3.7/copy.py", line 274, in _reconstruct
    y = func(*args)
TypeError: function takes exactly 1 argument (0 given)
>>> deepcopy(dtu.tzinfo)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.7/copy.py", line 180, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/usr/local/lib/python3.7/copy.py", line 274, in _reconstruct
    y = func(*args)
TypeError: function takes exactly 1 argument (0 given)
>>> # compared to e.g. pytz as tzinfo
... tz = pytz.timezone('Europe/Helsinki')
>>> dt = tz.localize(dtu.replace(tzinfo=None))
>>> deepcopy(dt)
datetime.datetime(2018, 7, 6, 19, 0, 32, 153444, tzinfo=<DstTzInfo 'Europe/Helsinki' EEST+3:00:00 DST>)

Using e.g. pytz as tzinfo works fine. Using: Python 3.7.0 udatetime 0.0.16

[Delgan]

@freach This seems to be a significant problem, being able to copy datetimes is important.

Any plan to fix it? Do you accept PR?