Crystals

-------------

* Added the ability to read and write POSCAR files from the Vienna Ab initio Simulation Package (VASP). Contributed by Chenxing Luo (8).

-------------

* Releases are now automatically performed using Github Actions
* Fixed an issue where uncertainties in atom site occupancy in CIF files would not be parsed correctly (7).

-------------

* The distinction between :class:`Supercell` and :class:`Crystal` no longer exists; :class:`Supercell` objects can be used everywhere a :class:`Crystal` is expected.

-----

* Starting with this version, ``crystals`` is licensed under GPLv3.
* General purpose single-crystal structure indexing with the DirAx algorithm has been added: :func:`index_dirax`.
* :meth:`Lattice.scattering_vector` and :meth:`Lattice.miller_indices` now accept tables of reflections/scattering vectors. This calculation is vectorized using NumPy.
* Migration of testing infrastructure to pytest.
* `Support for Python 3.6 and NumPy<1.17 has been dropped <https://numpy.org/neps/nep-0029-deprecation_policy.html>`_

-----

* The sorting of `AtomicStructure` objects is now stable.
* Fixed an issue where checking the containership of atoms did not work properly.
* Fixed an issue where downloading structures from the Materials Project failed on macOS/Linux.
* Code snippets in documentation are now tested for correctness.
* Tests are now included in the package itself.

-----

* Fixed deprecations that came with Python 3.9, involving comparison of crystal structures.