Provide a tox plugin

[Cadair]

Thanks for the awesome helper package.

I think that without a huge amount of work a tox plugin for this could be developed so that all you have to do is set a config flag for an env and it uses this package to compute the dependencies to install.

[WilliamJamieson]

This has been on my TODO list. Hopefully, I can get to it sometime in the future. If you figure out how to do this feel free to contribute it back.

[Cadair]

I will keep it in mind if I find the time, but my next couple of months aren't exactly looking like "quick foray into infrastructure" months.