FingerprintMols.py: set this up so that it can be called without arguments
AlignDepict.py: doc updates
Torsions.py: support the IntVect datastruct used by Pairs.py
Pairs.py: fix a bug with the fpLen, error checking on fp sizes and returning BitVects
AllChem.py: import the reactions code, add convenience wrapper GenerateDepictionMatching3DStructure