PaymentGateway::Request & PaymentGateway::Response

PaymentGateway::Request prepares the form params for redircting to
the payment gateway including a cryptographic signature

PaymentGateway::Response validates the incoming request as redirected
by the gateway. This includes verifying the cryptographic signature
and providing convenience methods to reveal pertinent information
from the response
git mv PaymentGatewayCheck PaymentGateway