Use `bashbrew` to gather the canonical list of supported suites

[tianon]

This is an attempt to help codify #162, and make sure that it's correct / mostly automated. I'd love to figure out a clean way to help @docker-library-bot be able to make these kinds of updates automatically, but that's a much larger/more complicated problem.

I'm not 100% sold on it, especially how fiddly and frankly unapproachable my filtering method is.