Remove cite.py

[bdice]

Feature description

For the 2.0 release, we should update or remove cite.py. My vote is to remove cite.py, since we don't have a standard across our Glotzer group software, there isn't a clear Python packaging standard (see links at bottom), and we have both a CITATION.cff file and a page in our documentation.

Proposed solution

If we remove it:

• Deprecate the functions in 1.x. See #611.
• Remove the module in 2.x (including references in api.rst and __init__.py). See #594.

If we choose to keep it: (we're removing it)

• Update docstring formats to NumpyDoc.
• Use the same citation as we recommend here (not an outdated arXiv citation that existed before the JCMS paper): https://docs.signac.io/en/latest/acknowledge.html
• Add tests for the cite functions (it is currently untested).

Additional context

GitHub recently added a button to our repository that uses data from CITATION.cff: https://docs.github.com/en/github/creating-cloning-and-archiving-repositories/creating-a-repository-on-github/about-citation-files

There is a long discussion of Python citation formats here that may provide alternative ideas: https://discuss.python.org/t/convention-for-encouraging-citation-of-python-packages/1764/1