• Added angle_tolerance to CifWriter.
• Change default float precision in CifWriter to 8. Adds float_prec kwarg to
  allow setting of arbitrary precision.
• Rudimentary pymatgen.io.vasp.help.VaspDoc class for obtaining help from VASP wiki.
• Massive documentation cleanup.
• Reorganization of Entry, ComputedEntry (@ayushsgupta).
• Bug fix for PourbaixDiagram (@montoyjh).