Make callback look at both GET and POST params so that sellers can also use the Header Redirect return method.
Add currency code parameter so sellers can price in multiple currencies.
2Checkout no longer has a seperate URL for the single page checkout routine.
Adding support for Direct Checkout
https://www.2checkout.com/documentation/checkout/direct-checkout/
Merge pull request #639 from craigchristenson/master

2Checkout new features