cli/args: add formulae_paths helper.
cli/args: add formulae_paths helper.

This allows getting the formulae passed as arguments while not having
to read the file or raising an exception on invalid syntax.

MikeMcQuaid/brew,JCount/brew,claui/brew,JCount/brew,sjackman/homebrew,claui/brew,mahori/brew,EricFromCanada/brew,nandub/brew,konqui/brew,EricFromCanada/brew,konqui/brew,JCount/brew,EricFromCanada/brew,reitermarkus/brew,mahori/brew,sjackman/homebrew,Homebrew/brew,JCount/brew,Homebrew/brew,reitermarkus/brew,Homebrew/brew,vitorgalvao/brew,MikeMcQuaid/brew,vitorgalvao/brew,MikeMcQuaid/brew,vitorgalvao/brew,konqui/brew,claui/brew,mahori/brew,claui/brew,Homebrew/brew,reitermarkus/brew,MikeMcQuaid/brew,vitorgalvao/brew,EricFromCanada/brew,mahori/brew,nandub/brew,nandub/brew,nandub/brew,sjackman/homebrew,reitermarkus/brew,sjackman/homebrew,konqui/brew