Custodian v0.7.5

1. Major Custodian now exits with RuntimeError when max_errors or
   unrecoverable_error is encountered.
2. Added BadVasprunXMLHandler.

Improvements to VASP handlers.

1. auto_npar option in VaspJob now properly handles Hessian calculations.
2. WalltimeHandler now supports termination at electronic step (David
   Waroquiers).
3. Improved handling of BRMIX fixes.

Improvements to VASP and QChem error handling

1. Improved backwards compatibility for WallTimeHandler.
2. Improvements to VaspErrorHandler. No longer catches spurious BRMIX error
   messages when NELECT is specified in INCAR, and pricel and rot_mat errors
   are now fixed with symmetry precision and gamma centered KPOINTS instead.
3. Improved Qchem error handler (Xiaohui Qu).