Merge "Update comment on required fields for an event"

     * <dd>When inserting a new event the following fields must be included:

     * <ul>

     * <li>dtstart</li>

     * <li>dtend -or- a (rrule or rdate) and a duration</li>

     * <li>dtend for non-recurring events</li>

     * <li>duration for recurring events</li>

     * <li>rrule or rdate for recurring events</li>

     * <li>a calendar_id</li>

     * </ul>

     * There are also further requirements when inserting or updating an event.