def before_train_station_pop(station, escalator):
    # calculate the number of people waiting to depart on the train by the time the train arive.
    station.travelers_departing = station.travelers_departing + (escalator.rate * escalators.entering * station.train_wait)
    # number of people who have arived and want to leave.
    station.travelers_arriving = station.travelers_arriving - (escalator.rate * station.train_time
    # Get the total station population.
    population = station.pop
    return population

"""This module calculates the number of people in the station by the time the next train arives"""

def before_train_station_pop(station, escalator):
    """This function calculates the total number of people as a sume of people
    waiting to board the next train, and the number of people waiting to leave
    the station by the elebvators."""

    station.travelers_departing = station.travelers_departing + (escalator.rate * station.escalators_entering * station.train_wait)
    # number of people who have arived and want to leave.
    station.travelers_arriving = station.travelers_arriving - (escalator.rate * station.escalators_exiting * station.train_wait)

Simplify the function to calculate the platform population between trains
Simplify the function to calculate the platform population between trains

The function to calculate the change in platform population in the time
between trains was needlessly complex. It has now been simplified.

ref #17
