Add support for global and recurring calendar events

Little bit of wordsmithing:

> When an event is repeated, the `"number"` value specifies which recurrence is represented.  The original event will have a `"number"` value of `1`, the first recurrence will be numbered `2`, and so on. The details of the original event, such as its ID and API URL, are included with recurrences. Recurrences do not have their own IDs or URLs.