Rename package to `factorum`

[jbiggsets]

For the next release, let's rename the package to factorum.

[desilinguist]

We'll have to figure out what to do about the existing packages. Do we just abandon that one or do something more specific? This might be a good reference: https://www.dampfkraft.com/code/how-to-deprecate-a-pypi-package.html

Redirect seems like a good option? I wonder if anaconda.org allows something like that.

[jbiggsets]

Cool. I will take a look!

[desilinguist]

This is no longer on the roadmap.