I see the possibility of these Formulary methods allowing us to do some more radical changes to brew, on the way to brew2.

Specifically, we can experiment with alternate, non-class definitions for formulae:

```
formula 'Thing' do
end
```

The 3 methods below can be updated to work either classic class-defined formulae or new DSL-defined formulae, which wouldn't eat into the Class namespace. (See the readline / brew debug hacks for why this is a problem.)