A model for a Kernel using homogeneous coordinates to represent the
geometric objects. In order for Simple_homogeneous<RingNumberType> to model Euclidean geometry
in E^{2} and/or E^{3}, for some mathematical ring E (e.g.,
the integers ℤ or the rationals ℚ), the template parameter RingNumberType
must model the mathematical ring E. That is, the ring operations on this
number type must compute the mathematically correct results. If the number
type provided as a model for RingNumberType is only an approximation of a
ring (such as the built-in type double), then the geometry provided by
the kernel is only an approximation of Euclidean geometry.

In contrast to Homogeneous, no reference counting
is used internally. This eases debugging, but may slow down algorithms
that copy objects intensively, or slightly speed up others.