GitLab

See https://simtk.org/forums/viewtopic.php?f=161&t=6512&p=16820#p16820 for more
information

See http://docs.openmm.org/development/api-python/generated/simtk.openmm.mtsintegrator.MTSIntegrator.html#
for the rendered results that are less than ideal.

Also changes a bunch of old-style Python classes to new-style (Py3 only has the
latter)

mm.GBSAOBCForce as well.

Previously, parameters were defined in multiple places -- amber_file_parser.py
and charmmpsffile.py.