Represent a ring as a substructure of a molecule

 Chemistry::Ring provides some basic methods for representing a ring. A ring
 is a subclass of molecule, because it has atoms and bonds. Besides that, it
 has some useful geometric methods for finding the centroid and the ring
 plane, and methods for aromaticity detection.
 .
 This module does not detect the rings by itself; for that, look at
 Chemistry::Ring::Find.