Test and Documentation Dependencies

As these packages are only needed for testing or building the docs and

not needed by end-users, we can be more aggressive about dropping

support for old versions. However, we need to be careful to not

over-run what down-stream packagers support (as most of the run the

tests and build the documentation as part of the packaging process).

We will support at least minor versions of the development

dependencies released in the 12 months prior to our planned release.

We will only bump these as needed or versions no longer support our

minimum Python and numpy.