QCflow 0.5

[TristanSJones]

New additions:

1. xTB for QCflow:

   • xTB calculates the geometry of a molecule
   • Psi4 then calculates the electronic properties in a single-point calculation from the xTB geometry

2. Psi4 is fully implemented:

   • geometry optimisation and single point calculations
   • geometry optimisation from pre-defined psi4 geometry
   • reorganisation energy calculations

3. Other changes:

   • updated documentation for all new functions
   • updated examples for new functions
   • fixing installation bugs seen within QCflow.yml file that caused long hang times
   • changing tests and documentation to be run through micromamba rather than conda to speed things up