A sha256 hash of the previous download is stored and compared with
new downloads before updating :latest casks. This prevents unnecessary
reinstalls when the cask hasn't been updated.
Move download path to cask from installer to prevent unnecessary
redownloads of casks.
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.