ENH: Point charge embedding and QMMM functionality in Turbomole calculator
Adapted the documentation and added two test scripts.
New properties: charges, point charge gradients
New parameters: 'esp fit'
New methods: embed
(as required by class Embedding in qmmm.py), get_charges
, read_charges
, get_forces_on_point_charges
, set_point_charges
, read_point_charges
New class: PointChargePotential (as required by the Embedding class in qmmm.py)