The Whitelist class provides a client for reading in
a set of integers from a file; reading in a sequence of integers
from standard input; and printing to standard output those
integers in the whitelist.
For additional documentation, see Section 1.2 of
Algorithms, 4th Edition, by Robert Sedgewick and Kevin Wayne.
Reads in a sequence of integers from the whitelist file, specified as
a command-line argument. Reads in integers from standard input and
prints to standard output those integers that also appear in the file.