`Base` is how you can tell I've been doing much rails lately ;)

I started off without the factory method and having `DeprecationFormatter` extend `Forwardable` and delegate to `File`/`IO` variants, but I was having a hard time pulling it apart that way, and perhaps delegation wasn't quite the right idea, so I scrapped it.

After having gotten it working this way I might be able to go back and work out a better composition approach, but I wanted to at least get this progress up to get feedback.