The Dihedral class

This class is used to generate functors which can be applied to graphs. We want to be able to apply all operations in the relevant dihedral group to a graph. The class has one member, element, which describes which element of the group to apply. In the group of order 2 * n, the first n elements are rotations, and the second n are reflections. When the constructor is called, an element number can be passed to select which element to apply. Then when the functor is called, the transformation corresponding to this element is applied to the graph passed to the functor.