Containment uses the sumOfTri to determine if a point is inside of the
rectangle, r1. It checks all four points of r2 (p1, p2, p3, p4) against
r1. If they are all inside, then the rectangle is contained.
To determine the size of rectangle, it was required to be able to
determine who would be the neighboring points. A neighbor is a point
that would make the exterior of the rectangle, not the cross-section.
Finding the neighbors allows for a simple l*w to calculate size.
defined what a rectangle is and also implemented IsRect(), which returns
a bool whether the coordinates given make a rectangle or not. Tests
were written for IsRect()
