Base class for for any object for which object.stream(DaylightObject::Atom)
and object.stream(DaylightObject::Bond) will return a stream of atoms and
bonds, respectively.
Chiral value values are 'None', 'Tetrahedral', 'TetrahedralAl', 'SquarePlanar', 'TrigonalBipyramidal', 'Octahedral', 'TetrahedralAnticlockwise', and 'TetrahedralClockwise'