Let's hide implementation detail on where to find alias directory.
This will benefit future core code and formulae separation.
Also let `brew readall` check aliases for all taps.
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.