Changes for 6.0
*Updated country list and fixed country names that were invalid to the USPS and thus failed to return rates.
*Rewrote domestic and international quotes into separate functions since they each require different code.
*Rewrote the code for decoding rates to use the XML_unserialize class provided by the UPSXML contribution. This greatly simplified decoding the XML responses returned by the USPS rates server.
*Changed international handling so that each international shipping method could have it's own handling fee as was previously done with the domestic methods.
*Changed the configuration for available shipping methods and handling fees to install based on the shipping methods found in the usps function. In the future if the USPS changes methods, a simple change of the methods listed in the usps function followed by a remove and reinstall of the module will update the configuration for available methods and handling.
*Added ability for handling to be per package or per shipment.
*Added packaging support since the USPS now requires package sizes as part of the rate request. The module has a simplified version of estimated packaging based on weight built in, and it can also use the full packaging support made available by the UPSXML contribution if that is installed.
*Eliminated entry of a USPS password as this is no longer used by the USPS rates server.
*Added ability to display Signature or Delivery Confirmation if these options are used.
*When using USPS insurance, the module will now quote insurance for the maximum of either the package value or the maximum insurable value for that shipping method and destination. For instance, if the package is worth $800 and the maximum insurable value for the method to the chosen destination is $675 then the module will return a rate including insurance for $675. Previous versions would not include any insurance at all in that case.

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