Port over diffractomer from the old cme_utils repo

[chrisjonesBSU]

While Freud does have diffraction modules, I still think it would be useful to port over the "old" diffractometer code into this repo.

[chrisjonesBSU]

If/when we get around to doing this, we have to keep in mind the license we use for this repo. See #39 for details.

[jennyfothergill]

Alternatively, that code could live in GIXStapose, which already has much of the diffractometer code and a BSD license.