print-point from book. [2.2]
Basic constructors and selectors. [2.2]
Midpoint function. [2.2]
Print segments too. [2.2]
Merge branch 'ex2.2'
Write interface for rectangle. [2.3]
First implementation of rectangle. [2.3]
Second implementation of rectangle to same interface. [2.3]
Merge branch 'ex2.3'