Fix doc build

[hakonanes]

Description of the change

Doc builds are failing (see e.g. here)... They also failed for kikuchipy recently. I fixed this by installing a pandoc version compatible with nbconvert (nbsphinx dependency). (See here.) This PR installs an nbconvert-compatible version of pandoc.

Edit:
That's apparently not it. Errors and solutions found:

• Initial doc build didn't pass reading of sources for orix.plot.AxAnglePlot. Apparently, the set() method inherited from Matplotlib's Axes class is not considered an inherited method. Sphinx therefore attempts to list this method in the API reference. This now fails. I've therefore explicitly excluded set() methods from the API reference for a class.

Progress of the PR

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

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.

[harripj]

LGTM @hakonanes thanks for taking the time to implement the fix!

[hakonanes]

Thank you for the quick review!