Added init.py
By default, do not force symmetry upon protons attached to same heavy atom.
Updated adjacency graph calculation to symmetrize.
Added basic logging.
Added logger to test-drugs.py
Use no constraints in test-drugs.py.  Noted this requirement in SystemChecker docstring.
Use no constraints in test-drugs.py.  Noted this requirement in SystemChecker docstring.
Check for zero force constant when comparing harmonic angle forces.
Take care not to divide by zero charge when calculating relative error.
Merge pull request #6 from kyleabeauchamp/fixing_drugs

[WIP] Starting work to fix drugs...