basic support for obtaining UPS shipping labels
rename obtain_shipping_labels to create_shipment to match canada post. Allow options to select units that don't match origin country's default.
Merge pull request #176 from CasperSleep/ups_shipping_labels

Basic support for obtaining UPS shipping labels (Rebased)
Handle fedex nil response status node
Describe inches in the metric primitive unit so it initializes correctly
added test
Merge pull request #177 from Shopify/handle_fedex_nil_response_status_node

Handle fedex nil response status node
Merge pull request #178 from Shopify/quantified-in-primtives

Describe inches in the metric primitive unit so it initializes correctly
Use passed in commercial_base option
Don't allow negative grams items to put packer in an infinite loop
Merge pull request #181 from Shopify/shipment-packer-infinite-loop-fix

Don't allow negative grams items to put packer in an infinite loop
Merge pull request #182 from Shopify/usps-options-commercial

Use passed in commercial_base option for USPS