better error messages for invalid partial args to new
add "description" to ::Package
fix parsing Receipt/Image
customer_context everywhere
return shipment tests
v1.0.7

 - fix parsing receipt image for ship_accept calls on return shipments
 - packages now have a 'description' field, which is required for
   return shipments
 - better error messages when constructing credit cards and services
   with just the code or just the label / type, and an invalid value
   is passed
 - add 'customer_context' to all response objects