A Singleton describes an object class that can have only one instance 
in any system.  This module implements a Singleton class from which
other classes can be derived. By itself, the Class::Singleton
module does very little other than manage the instantiation of a
single object. In deriving a class from Class::Singleton, your
module will inherit the Singleton instantiation method and can
implement whatever specific functionality is required.

For a description and discussion of the Singleton class, see
"Design Patterns", Gamma et al, Addison-Wesley, 1995, ISBN 0-
201-63361-2.