Send webhook request in /paypal/ipn
Only send webhook request when answering a /AdaptivePayments/Pay IPN message
Simplify the callback result returned from Iron#enqueue
Refactor, extract a new method Payment#composeWebhook
Refactor, be optimistic on Payment#execute
Add tests for method Payment.executeSingle, Payment.authorize
Send a webhook when executing a recurring payment
Only execute recurring payments with status 'ACTIVE'
Extract a new method Payment#_updateBilling
Refactor on tests, wrap calls to before / after within `describe`
Set the status of payment to 'COMPLETED', when nextBilling > endingAt