Ability to create a UPS return label
Ability to create a UPS return label

  - Create a return label by setting the return_service_code
  - list of return service codes for reference
  - units used are now always based on shipper's country,
    allows international return from a different country than shipper
  - don't include SoldTo when it's a return
  - return requires a description at the package level

Shopify/active_shipping,Goldbely/active_shipping,johannboutet/active_shipping