This update takes into account the new changes in the USPS API where the First-Class Shipping options were no longer showing due to a name change from First Class Mail Parcel or First Class Package Service to First Class Package Service -Retail for retail pricing.

It also will now filter for the weight limits allowed by commercial vs retail on small packages and cleans up the admin listing or first class options. 

For zen cart versions 1.5.0, 1.5.1, 1.5.2, 1.5.3, 1.5.4, 1.5.5+, 1.5.6+, 1.5.7+