Executive class to control a 3 phase simulation in which entity records are
held in a Vector (details) and from which a temporary Vector (dueList) is
created at each time beat to contain those entities with events due at the
current event time.
Contains the Cs, initialisation and finalisation for a 3 phase simulation
of the Harassed Booking Clerk problem introduced in Pidd (1998) Computer
Simulation in MAnagement Science, John Wiley, Chichester.
Used to represent simulation objects that need not be represented as
individual entities since they are identical and can be taken and returned by
objects that are represented as entities.