ProcessArrival function
1. Update number of arrival statistics.
2. Output a message with current time and event.
3. AtHead = True is Line is empty.
4. Add an Arrival event to Line.
5. Delete an event from Event list since it is being processed now.
6. If (AtHead) // start the processing first person
Insert in the Event List a Departure Event for CurrentTime+TransTime of current event;
7. Get Next Arrival from Input File; Update Event List.