Refactor Cask’s extensions.

Library/Homebrew/cask/lib/hbc.rb

Library/Homebrew/cask/lib/hbc/artifact/artifact.rb

Library/Homebrew/cask/lib/hbc/artifact/pkg.rb

Library/Homebrew/cask/lib/hbc/artifact/relocated.rb

Library/Homebrew/cask/lib/hbc/cli.rb

Library/Homebrew/cask/lib/hbc/extend.rb

Library/Homebrew/cask/lib/hbc/extend/string.rb

Library/Homebrew/cask/lib/hbc/system_command.rb

Library/Homebrew/cask/lib/hbc/utils/hash_validator.rb

Library/Homebrew/diagnostic.rb

Library/Homebrew/extend/io.rb

Library/Homebrew/extend/optparse.rb

Library/Homebrew/test/test_diagnostic.rb