Consider making use of xtb's --json flag

[matterhorn103]

Using --json results in some results being saved to xtbout.json. Reading and handling the results in JSON format would naturally be easier than manually parsing the output text file.

Unfortunately geometries are not printed to it, and information for frequencies and orbitals is not complete enough to use instead of g98.out (missing the atomic displacements for the former and the basis set and orbital coefficients for the latter).

So currently it would only really be useful for getting the energy without parsing the output file as a text file.

Other results printed to the file include:

• HOMO-LUMO gap
• molecular dipole
• partial charges
• atomic dipole and quadrupole moments

I don't think many of these are currently supported by CJSON or Avogadro. Possibly partial charges are.