The usps shipping calculators in this gem seem to be out of date. This PR does the following:
Add different service_code prefix for domestic and international rates because the code returned from usps API is not mutally exclusive between domestic and international rates. e.g. service_code "1" is priority mail for domestic and express mail for international. With the prefix we can now distinguish them.
Add two new shipping rates: GlobalExpressGuaranteed and StandardPost
Bug fix (check AVAILABLE_COUNTRIES instead of undefined WEIGHT_LIMITS in a few places)
The usps shipping calculators in this gem seem to be out of date. This PR does the following: