#87 Non-tetrahedral chirality

[Geoff Hutchison]

Chirality is not limited to tetrahedral atom geometries. In particular,
SMILES and SMARTS formats (among many others) support more
complicated chirality and search queries.

The current chirality framework should be expanded to handle and
enumerate non-tetrahedral chiral environments.

e.g.:
http://www.daylight.com/smiles/smiles-isomers.html#GENCHI

[Geoff Hutchison]

I'm re-assigning this to Tim, since he was working on this. I don't know that the SMILES standard is defined well-enough for this. Perhaps we should revisit with Craig for the OpenSMILES implementation?