Added support for iPay88 integration
Swap service_url and entry_url to play nice with ActiveMerchant's payment_service_for view helper
swap entry and service url.
Ipay88 comment cleanup.
credentials are not set as class variables, change to pass the merchant key into initialize
Fix endpoint url, customer name
Fix a couple tests
SecureNet: Use the live_url at the right time

I'm so surprised this gateway wasn't using the live_url yet!

Closes #792.
New IATS Gateway
ActiveMerchant::Billing::Base.gateway raises when passed an invalid gateway
Merge pull request #794 from Shopify/billing-gateway-raise

ActiveMerchant::Billing::Base.gateway raises when passed an invalid gateway
Merge pull request #788 from Shopify/ipay88

Ipay88 integration
MerchantWarrior: Fix handling of amounts

The gateways can take in a Money or an integer in cents.  Then under the
covers it sends the amount in the right format to the actual gateway.

The Merchant Warrior gateway class was taking in a string dollar amount
rather than behaving like the other gateways.
Merchant Warrior: Send the CVV to the gateway

Closes #795.
Fix status messages for PayU.
Merge pull request #793 from Shopify/add_iats_gateway

New IATS Gateway
Merge pull request #799 from Shopify/fix-payu-status-types

Fix status messages for PayU.
SecureNet: Allow production transactions

The TEST parameter was always being sent as true!  Now we only pass that
parameter at the right time.

Closes #805.
updated unit tests to reflect use of fetchCurrencyCodes API to find supported currencies. All passing.
added more documentation, implemented supported_currencies method