Deprecate some contributions.

This is just a starting point to start discussion. I think we have a
few options with contributions:

- Stop accepting them altogether and move the ones we need/use/support
  into core commands
- Accept them on an unsupported basis and require they be added
  manually to the PATH
- Actively support and fix bugs in them all

Thoughts?
Yup, that's cool with me. I guess I'm just interested in a bit of discussion on the initial PR description; perhaps let's make @jacknagel's version a core command.