v4.0.0

• Bumps minimum Ruby version from 2.2 to 2.5
• Bumps dev dependencies
• Documents each interface of the project in code
• Overhauls the test suite with full coverage
• Introduces Rubocop and lints the entire project
• Removes the unusable Print and PrintJob objects
• Removes deprecated and unusable stamp_and_barcode_by_reference method on the Batch object
• Explicitly returns an error of "not implemented" for Rate.all and Parcel.all
• Removes the Shipment.get_rates function as shipments already contain rates. If you need to get new rates for a shipment, use the Shipment.regenerate_rates function instead
• Removes the parameters from Address.verify as they are unusable
• Removes the deprecated http_status property of the EasyPost::Error object as it was replaced with status
• Fixes a bug that would append an extra id field to each retrieved object
• Various other small improvements and bug fixes