Add Vector3d.scatter() reproject onto hemisphere functionality

[harripj]

Description of the change

As discussed with @hakonanes in #306 (comment)

This is just an idea for the future, but it might be that we should support a boolean parameter to Vector3d.scatter() to set whether vectors on the other hemisphere (northern if hemisphere="south is passed and vice versa) should be projected up to the projection plane as well. We should then force the scatter points to be different.

We should include the option to reproject vectors onto the visible hemisphere, ie. if Vector3d.scatter(hemisphere='upper') is called then vectors projected onto the lower hemisphere are not shown. This PR adds the reproject argument to Vector3d.scatter() which reprojects vectors located on the hidden hemisphere to the visible hemisphere. This is achieved by reflection of the vectors in the x-y plane.

The reprojected vectors are displayed with a '+' marker by default and can be set using the reproject_marker argument. If hemisphere='both', reproject=True has no effect as all vectors are already shown on one of the two axes.

If approved the changes in this PR should be used to simplify #306.

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

from orix.quaternion import Orientation, symmetry
from orix.vector import Vector3d

o = symmetry.O * Orientation.random()
v = o * Vector3d.zvector()

v.scatter(hemisphere='upper', show_hemisphere_label=True)

v.scatter(hemisphere='upper', reproject=True, show_hemisphere_label=True)

reproject=True has no effect if hemisphere='both':

v.scatter(hemisphere='both', reproject=True, show_hemisphere_label=True)

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.

[hakonanes]

Just ping me whenever this is ready for review.

EDIT: I typically use the "Mark as draft" and "Mark as ready for review" functionality.

[hakonanes]

This is a very nice addition to the scatter() convenience plotting method! I've made some requests. I think a mention of this possibility in the stereographic projection user guide should be added. Perhaps it is most suitable to add it to the end of the "Upper and/or lower hemisphere" part (here)?

[hakonanes]

Thanks for the docstring improvements and addition to the user guide. I've got a few more requests before approving.