Numpy-like flattening

[argerlt]

CUrrently unfinished, but when it's done, this This PR addresses and should close #595 once finished.

Main remaining task is to add an order parameter to all the functions that run super.flatten()

To give some scope to this problem, pytest raises 191258 warnings in htis PR. That's enough that we should probably add a filter inside Object3d.

Progress of the PR

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

Minimal example of the bug fix or new feature

For reviewers

• The PR title is short, concise, and will make sense 1 year later.
• New functions are imported in corresponding __init__.py.
• 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.

[argerlt]

pre-commit.ci autofix

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