Use Engine.routes.prepend

Instead of Engine.routes.draw so that Spree core routes are always
loaded first

[Fixes #68]
removed raise ShippingError from compute, fix #90
moved Error logic to the Order model on rate_hash
Merge pull request #91 from mrpollo/1-3-stable

removed raise ShippingError from compute, fix #90
usps api name changes fix #103
moving from matching service names (desc) to checking for service codes
in order to achieve this it was necessary to override compute and
retrieve rates from Spree::Calculator::Shipping::ActiveShipping::Base on
Spree::Calculator::Shipping::ActiveShipping::Usps::Base
I added a service code paramter to all the usps classes and made sure
it was the correct id, please refer to this issue for further
explanation: https://github.com/spree/spree_active_shipping/issues/103
Use a real gem source in Gemfile
usps api name changes fix #103 moving from matching service names (desc) to checking for service codes in order to achieve this it was necessary to override compute and retrieve rates from Spree::Calculator::Shipping::ActiveShipping::Base on Spree::Calculator::Shipping::ActiveShipping::Usps::Base I added a service code paramter to all the usps classes and made sure it was the correct id, please refer to this issue for further explanation: https://github.com/spree/spree_active_shipping/issues/103

Fixes #106
Merge pull request #106 from mrpollo/1-3-stable

usps api name changes fix #103