Implement get_shipments using new REST API
Implement add_shipment using new REST API

NOTES:

* Order total is no longer supported (apparently it's calculated)
* Options (for line item products) no supported (not information on this in the documentation)
Clearer spec errors
Use credentials from env
Upgrade /update_shipment webhook
bump endpoint_base
latest jbuilder doesn't load activesupport anymore
endpoint_base takes care of unhandled exceptions
clean up not used / repeated code
spec for order not found on /update_shipment
update vcr cassetes
Abstrac api calls to custom client

so we deal with not 200 in one place only and raises properly
implement pending specs
Rename `headers` to avoid conflicts with sinatra / hack interface
shipment.id maps to orderNumber not orderId in shipstation
Return full shipment object in a shipstation key
Merge branch 'rest-api'

Conflicts:
	shipstation_app.rb
drop key no longer supported in specs