Class `Circle`

is defined in `circles.web`

.
It is derived from `Ellipse`

, using public derivation.

Since `Circle`

is just a special kind of `Ellipse`

, there is
often no need to define special functions for `Circles`

.

Currently, `Circle`

inherits the transformation functions and
`operator*=(const Transform&)`

from `Ellipse`

. Consequently,
the data member `radius`

, described below,
is not recalculated, when transformations
are performed on a `Circle`

. I plan to change this soon!