This makes using `HOMEBREW_CURL` significantly nicer as then the system
`curl` (that, on old versions, sucks at SSL) can download a version of
`curl` that it can build from source.
This is the (partially) documented public API for Homebrew.
The main class you should look at is the {Formula} class (and classes linked from there). That's the class that's used to create Homebrew formulae (i.e. package descriptions). Assume anything else you stumble upon is private.