Merge pull request #2 from eileenmcnaughton/master

worked on Authorize Request
Merge pull request #3 from eileenmcnaughton/master

Some work on completePurchase here
added completeAuthorize message classes and a signature method to the gateway
added some getters used when validating response
fix purchase transaction_type to sale
check signed data on request response
fix getTransactionReference function to refer to correct field