Complete freud examples repository

[Bradley Dice]

From our roadmap planning session, @vramasub and @bdice identified several ways to provide improved freud examples. This would be a good task to share between @bdice, @harperic, and module authors.

• Create Jupyter notebooks that provide tutorials for each module
  • Should be complete enough to show all module features, and copy-pasteable for new users or quick snippets
  • Secondary goal is to make figures that would be suitable for publication
  • Notebooks belong in separate freud-examples repository
  • Once created, insert notebooks directly into an Examples section of the docs using nbsphinx, see https://signac.readthedocs.io/en/latest/signac_101_Getting_Started.html for example

[Bradley Dice]

This is nearly done.