pdt256/shipping — pull request #5 by perk11 (2014-12-07 10:06:48+00:00)
Title: Automatic calculation of size for USPS

As [specified in docs](https://www.usps.com/business/web-tools-apis/rate-calculator-api.htm#_Toc378922331), there are 2 shipment sizes, and they are based on dimensions that we already know. "Size" is a required field, but we can calculate it automatically.

Also removed duplicate setting of username.