Split nimi-python documentation and ReadTheDocs project

[ni-jfitzger]

Split our documentation and ReadTheDocs project to support package version independence. We can't have separate versions if our documentation only has one version for the whole repo.

[ni-jfitzger]

Doing this does not force us to use independent versions for our packages. Thus, as long as we continue to use the same versions, we don't have to handle the changes necessary for version independence at the same time.