Make `tz` default to `datetime.timezone.utc` to allow for less verbose code.
0.4
Changed `FreezeTime` interface to receive the system's datetime and the system's timezone, and mock the behavior of `datetime` and `time` based on those attributes.
FreezeFrog now officially supports both `datetime` standard timezone objects and `pytz` timezone objects.
0.3
Fixed an issue where `tz_delta` wouldn't be properly cleaned up when exiting the context manager 6