Teachpacks for How to Design Classes

# A Geometry Library (HtDC)

###

This `geometry` package provides a class for representing positions in a Cartesian world:

                          +----------+
                          | Posn     |
                          +----------+
                          | int x    |
                          | int y    |
                          +----------+

To create an instance of the `Posn` class, a program must supply two `int` values: one for its x coordinate of the canvas and the second for its y coordinate.