Log Message:
Update to 2.4.0:

Version 2.4.0
-------------

- Fix an issue with relativedelta and freezegun (lp:1374022)
- Fix tzinfo in windows for timezones without dst (lp:1010050, gh #2)
- Ignore missing timezones in windows like in POSIX
- Fix minimal version requirement for six (gh #6)
- Many rrule changes and fixes by @pganssle (gh pull requests #13 #14 #17),
    including defusing some infinite loops (gh #4)