Adds new attendees to the event.

    *attendees* can be a list of email addresses or :class:`ExchangeEventAttendee` objects.

def add_attendees(self, attendees, required=True):
    """
    Adds new attendees to the event.

    *attendees* can be a list of email addresses or :class:`ExchangeEventAttendee` objects.
    """

    new_attendees = self._build_resource_dictionary(attendees, required=required)

    for email in new_attendees:
      self._attendees[email] = new_attendees[email]

    self._dirty_attributes.add(u'attendees')