Support Reversal Request (void) and Partial Refund (refund)

Thank @siewmai for making these features possible. Now you can use $gateway->void($options) to request a reversal of transaction or $gateway->refund($options) to request full/partial for a 'captured' or 'settled' transaction.

Update to make compatible to the latest spec

Thank @siewmai for making this library compatible with the latest MOLPay Specification 13.7 (10 Oct 2017)

Add fallback mode for pre-sKey / sKey generation

MOLPay doesn’t quite certain of their currency format, thus we have to make a fallback for the second attempt.

Remove isCallbackNotification

• Fix currency issue
  MOLPay returns currency as 'RM' instead of 'MYR' causing the skey generation failed.
• Remove isCallbackNotification
  Remove callback notification as it should not be part of Omnipay, user should handle it themselves.

Remove isCancelled check

• Fix isCancelled checking - previous isCancelled checking was depend on status '11' from MOLPay but there was a mistake as status '11' is indicating an error payment but not cancelled payment.

v2.0.0

First working project