This program illustrates the use of the STL stable_sort() algorithm (default
version) to sort Points, where one Point comes before another if and only if
its x-coordinate is less than the x-coordinate of the second Point.

An interesting exercise is to change the call to stable_sort() to a call to
sort() and observe the difference in output, if any.
Press Enter to continue ...

Here are the contents of the vector:
(2,4) (2,3) (5,5) (3,7) (3,5) (1,2) (1,1)
Press Enter to continue ...

And here are the contents of the sorted vector:
(1,2) (1,1) (2,4) (2,3) (3,7) (3,5) (5,5)
Press Enter to continue ...