remove const specifiers from return values in DataStructs
add initial pass at query-query matching for Atoms and Bonds
fix and test for sf.net issu 2738320
add Mol.AddRecursiveQuery() method to Mol
instead of using the property map interface.
A nice side-effect is that the wart of having to use property maps to loop over bonds or atom neighbors
is now gone.
This potentially breaks lots of client C++ code.
GraphMol/DistGeomHelpers/:
Support generating random initial coordinates of atoms as an alternative to embedding. This has so far only been tested on windows (all tests pass) and it needs to be optimized (particularly force field parameters).
Other changes here are primarily cosmetic code cleanups.
