Returns an array of event ID's that are between the two given datetimes.
icap_list_events() function takes in a beginning datetime and an end datetime for a calendar stream. An array of event id's that are between the given datetimes are returned.
All datetime entries consist of an object that contains:
int year - year
int month - month
int mday - day of month
int hour - hour
int min - minutes
int sec - seconds