This code comes from Chapter 1 of the book "Refactoring: Improving
the Design of Existing Code", by Martin Fowler.  It is in the state
you see at the beginning of the chapter.

2010-05-13   Ported to Ruby for 810:188 (Summer 2010)    / Eugene Wallingford
2012-10-01   Ported back to Java for CS 2530 (Fall 2012) / Eugene Wallingford

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HISTORY

v0   The original code.
v1   Decomposed the statement() method, creating helper methods
     to compute prices and frequent renter points.
v2   Moved priceFor() and frequentRenterPoints() to the Rental class.
v3   Created htmlStatement() method and tests.
v4a  Moved priceFor() to the Movie class.
v4b  Created MovieCategory class and subclasses.
     Changed priceCode from int to Category.
v4c  Moved price() to the Category classes.
     @todo -- Moved frequentRenterPoints() to the Category classes.

@todo   Eliminate Movie price code constants.
@todo   Eliminate Movie public accessors