added stdlib dependency
refactored airdrop/all_interfaces_spec to use "ensure" and default paramater
refactor airport/disconnect_on_logout to use ensure and validate arg
validate args and use default arg in airport/join_mode
validate args and use defaulta arg in airport/join_mode_fallback
refactor airport/remember_recent_networks to use ensure, default arg, and validate arg
refactor airport/require_password_for_computer_to_computer_networks to use ensure, default arg, and validate arg
refactor airport/require_password_to_toggle_power to use ensure, default arg, and validate arg
refactor airport/require_password_to_change_networks to use ensure, default arg, and validate arg
refactor appearance/colors to validate args