Exercise Container Design and Robustness
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In this directory you find the following:

Trace.h  A helper class Tracer for producing output showing how objects are 
         created, copied and destroyed.

	 Tracer have a default constructor, a copy constructor, a copy 
         assignment operator, and a destructor, which outputs trace messages
         when called.

	 Tracer also have functions on() and off() for turning tracing on
	 and off, respectively. Default is on.

	 The member value is simulating the what we might actually want to
	 store, and used for outputting container content.

	 There is an overloading of operator<< for outputting Tracer objects,
	 i.e. the stored value of type T.

Here, Tracer is primarily used to find out, or verify, what functionality the
different versions och the container class puts on the contained type.