Vesta add energy landscape to data file

[stefsmeets]

The way to add multiple volumes would be something like this:

from pymatgen.io.vasp import VolumetricData

energy = volume.get_free_energy(temperature=1234)

vol_data = VolumetricData(structure=structure,
                          data={
                              'total': volume.data,
                              'energy': energy.data,
                          })

vol_data.write_file('vesta.vasp')

[stefsmeets]

Possible after #282 via :

energy = volume.get_free_energy(temperature=1234)

volume.to_vasp_volume(structure=structure, filename='volume.vasp, other=[energy])