v2017.11.6

• Better exception handling in EnumlibAdaptor and
  EnumerateStructureTransformation.
• Allow bypassing of ewald calculation in EnumerateStructureTransformation.
• get_symmetry_operations API convenience method for PointGroupAnalyzer.
• New DiscretizeOccupanciesTransformation to help automate ordering of
  disordered structures.
• Fix POTCAR check for POSCAR.
• Minor updates to periodic table data.
• Misc bug fixes.