Only show new formulae or casks when HOMEBREW_UPDATE_REPORT_ALL_FORMULAE
environment variable is set.
Stop checking for HOMEBREW_UPDATE_REPORT_ALL_FORMULAE when the key is
:R, :A or :AC in ReporterHub#dump_formula_or_cask_report because
that check is made redundant by the check in ReporterHub#dump.
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.