Use a JSON encoder that knows how to encode vDDDTypes as datetimes
Fix a bug in recurrence rules
- Take additional (rdate) and excluded (exdate) dates into account in recurrence rule sets
- Apply a default tzinfo to exdate and rdate rules based on the start/end date tzinfo. This is because the icalendar library does not retain the timezone info in the exdate/rdate rules. File a bug.