A query is a piece of topology, like a molecule, but nodes are
QueryAtoms and edges are QueryBonds.

QueryAtoms and QueryBonds are subclasses of QueryObjects

QueryObjects:

Different types exist:
  equality
  inequality (>,>=,<,<=)
  range (within a min,max range)
  set membership
  and
  or
  xor
all can be negated

can have child queries (not part of topology) to support (and, or, xor)

Include num_match and optional presence functionality (to allow "one
 or more", "maybe present"  etc.) so we can do wildcard searches:
  "does the molecule have two aldehydes separated by a chain of
   conjugated carbons"  (something like C(=O)[C=C]*C(=O))
  

QueryAtoms and QueryBonds have specific member data
(i.e. atomicNum, implicitValence, order, isAromatic, etc.).  

