Update pyproject.toml - add mdtraj dependency

[janpriessnitz]

Hi folks,

I recently installed py4vasp and it was missing 'mdtraj' package:

`File ~/.local/lib/python3.10/site-packages/py4vasp/_data/structure.py:8
5 from dataclasses import dataclass
7 import ase.io
----> 8 import mdtraj
9 import numpy as np
10 from IPython.lib.pretty import pretty

ModuleNotFoundError: No module named 'mdtraj'`

It should be listed in py4vasp's dependencies, right? Version 1.9.9 worked fine for me, so I put '>=1.9.9' version specifier into the PR. Feel free to edit the PR if you think an older version would be better.

Cheers,
Jan

[martin-schlipf]

mdtraj used to be a dependency but is not anymore in the current master. It can also not be reliably pip installed in particular on Windows and MacOS. The developers of mdtraj recommend to install it with conda and we found that more reliable as well.
These changes are already in documentation of the current master version but unfortunately not in the latest release. We plan to release a new version of py4vasp soon after the next version of VASP is released and then the documentation will reflect this as well.

[janpriessnitz]

I see! Thanks for clarifying.