Exclude executables in #empty_installation? to avoid 'Empty
Installation' error when only executable which name is the
same as one of metafiles is installed.
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.