service: provide formula accessor.
service: provide formula accessor.

Use `f` because it's generally recognised as a formula and this
shouldn't be widely needed/used.

Homebrew/brew,JCount/brew,MikeMcQuaid/brew,Homebrew/brew,MikeMcQuaid/brew,MikeMcQuaid/brew,nandub/brew,JCount/brew,MikeMcQuaid/brew,Homebrew/brew,nandub/brew,Homebrew/brew,nandub/brew,JCount/brew,JCount/brew,nandub/brew