Tim Moore

This is ready for another set of reviews. It especially needs a careful review of whether I correctly account for the patch cutoff when building the AABB around particle `i`...

I addressed Brandon's last round of suggestions, so I think this is good to go now.

@bdice I've figured out the origin of this bug in the code, which comes from how the k-vectors are generated, relevant lines [here](https://github.com/glotzerlab/freud/blob/ff9d561c2b8d719eea8e7167f083da3fbcc296a6/freud/diffraction.pyx#L257) and [here](https://github.com/glotzerlab/freud/blob/ff9d561c2b8d719eea8e7167f083da3fbcc296a6/freud/diffraction.pyx#L300). I need help figuring out...

@vyasr and @csadorf, is this still more appropriate as a 2.1 feature, or can it go into 2.0?

See also #96

@mturiansky is the `spec_trans` material property not what you are looking for?

@mturiansky I think it should work in a SceneView, but Qt widgets are notoriously finicky, so there may be something weird going on with different versions of different libraries.

My validation tests indicate that I introduced a bug in between my initial implementation and this pull request. Currently investigating.

I am interested, but since I don't have a research need for this at the moment I cannot commit to implementing it.

Now that I'm thinking about it, it should be fairly straightforward. Unless I'm missing something, shouldn't this consist of adding a variant to `UpdaterQuickCompress` and using that variant to compute...