v1: A first attempt at a Pair class.  For now, the fields are public,
there's one constructor and two getters, and everything else is default.

v2: We've added an explicit copy-constructor, an explicit assignment
operator, and an explicit destructor; all three of them, as well
as the regular constructor, print a message saying what they're
doing.  The regular constructor has been modified to default its
arguments to 0, which makes
	const Pair origin;
legal code in the main program.
To illustrate the creation and destruction of variables in local scope,
I've put several lines of the main program into a nested block; the
"result" variable is local to this block, so when we get to the end
of this block, the destructor is called on it.

v3: Added an == operator, implemented as a stand-alone function.
This function needs to see the fields of the Pair, so they need to
be public (or the operator needs to be a "friend", which we haven't
discussed yet).

v4: Re-implemented == as a method of the Pair class.  Since it's
in the class, it can now see the fields even if they're private,
so I made them private.

v5: Added a << operator so I can print out Pairs nicely.  Note that
since its left operand is an ostream, and we can't change that class,
this one MUST be implemented as a stand-alone function.  Since such
a stand-alone function can't see the private fields of Pair, I've used
the getters.
