Fix tzinfo is overidden by super's constructor default.
Add tests for timezone aware periods.
Fix Period subclasses' get_***_range methods to return appropriate
date ranges.
Add tests for commit 30ee804ce216
Ensure tzinfo propagation to subperiods.
Merge branch 'timezones'
Use an internal utc represantation. Period wont work with naive datetimes or dates.
Fix daylight saving time issue in periods.py
Fix tests for aware datetime objects.
Fix periods for naive datetime objects.
Improve Periods timezone robustness.
Merge pull request #41 from Pavlov123/master

Fix issue #14.