- fixed a bug in UFF/TorsionConstraint.cpp and MMFF/TorsionConstraint.cpp
  which caused issues with negative angles
- made also UFF/AngleConstraint.cpp and MMFF/AngleConstraint.cpp more
  robust against angle ranges involving negative values
- added relevant C++ and Python tests
Merge pull request #395 from ptosco/master

TorsionConstraint bug fix