how should dealing with multiple coordinate sets at the same time be done?
	Atom::getCoord has code to add Coord's if necessary.  Maybe this
	should broken into several functions?  want a getCoord that gets
	from the default coordinate set, a getCoord that gets from a
	particular coordinate set, and a makeCoord that adds a coordinate
	to all coordinate sets?

finish molgraph support when RFE's are done (Bond::otherAtom, and
	Atom::isBondedTo)

Error check that the Coord in CoordSet container be an "array"
	or indexed by "int"

document class description files
	finish allowing different kinds of iterators
	add support for templates of maps (should at least have error
		message right now)

ring support

more features:
	how to initialize new coordinates

In ~Molecule(), List's and Vec's don't have an empty() message.
In Atom::getCoord(), List's and Vec's don't have an empty() message.

change key function (rekey) for maps?

what about allowing more than one "use"?  For example, having a per-Residue
	map of Atoms by name and by atomic number.
