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Add the ability to reference casks from brew --cache and brew home.

brew --cache <cask> prints the cask's cached without any prefix.

brew home <cask> opens the homepage of the cask in the default browser.

With respect to the tests, I don't think I should reference a cask that exists as part of homebrew-casks, yet I cannot figure out how to add a cask such that it can be referenced by name from Cask::CaskLoader.load. I currently pass in the path to the local-caffeine cask. I'm relatively new to Ruby, so I'm not sure of all the factors in play here, but it appears tests/cask/cask_spec.rb:32 is able to reference local-caffeine without trouble, and I'm interested to learn why.