Add python_requires>=3.7 packaging metadata

[sk1p]

Description of the change

As a follow-up to #347, actually prevent installing on incompatible Python versions when using pip.

Note that currently, in a Python 3.6 environment, pip install orix will install an incompatible version (0.10.0) of orix. This is caused by the missing python_requires metadata - without it, the package is seen as compatible with any Python version.

Merging and releasing this won't magically fix things for 0.10.0 though - without yanking that release, installing orix in an old Python 3.6 environment will continue to pick 0.10.0 and fail at runtime. But adding this and updating once 3.7 support is dropped means the same issue won't come up again.

I'll leave the decision about yanking to the maintainers, of course.

Progress of the PR

• Docstrings for all functions
• Unit tests with pytest for all lines
• Clean code style by running black via pre-commit

For reviewers

• The PR title is short, concise, and will make sense 1 year later.
• [n/a] New functions are imported in corresponding __init__.py.
• [n/a] New features, API changes, and deprecations are mentioned in the unreleased
  section in CHANGELOG.rst.
• Contributor(s) are listed correctly in __credits__ in orix/__init__.py and in
  .zenodo.json.

[harripj]

@sk1p thanks for raising this and providing a fix. I would be in favour of yanking the 0.10 release once 0.10.1 is released soon (#390), as python 3.6 is unsupported for this release. What do you think @hakonanes @pc494 ?

[hakonanes]

Thank you very much for bringing this to our attention, @sk1p. Yes, we should yank 0.10.0 once 0.10.1 is out.

@sk1p, since this is a bug fix, can you branch of main instead and make a PR to that branch instead?

[sk1p]

since this is a bug fix, can you branch of main instead and make a PR to that branch instead?

Done! Nowadays possible via the edit button at the top btw.

[sk1p]

Done! Nowadays possible via the edit button at the top btw.

I guess I spoke too soon, as it included some unrelated changes. I'll fix this in a bit.

[hakonanes]

If it's OK with you @sk1p I'll push some updates to your branch adding you to the credits (taking relevant Zenodo metadata from the same entry in LiberTEM) and add a changelog entry.

[sk1p]

If it's OK with you @sk1p I'll push some updates to your branch adding you to the credits (taking relevant Zenodo metadata from the same entry in LiberTEM) and add a changelog entry.

Sure, thanks!