added status codes for pending, renamed other status codes

Pending is self explanatory. Renamed other status codes (`:user_cancellation` => `:cancelled`, `:request_timeout` => `:expired`) to match what is in Rabobank's PHP lib:

```php
// Translate transaction status code
protected function getTransactionStatus($sTransactionCode)
{
	if(in_array($sTransactionCode, array('00'))) // SUCCESS
	{
		return 'SUCCESS';
	}
	elseif(in_array($sTransactionCode, array('60', '90'))) // PENDING
	{
		return 'PENDING';
	}
	elseif(in_array($sTransactionCode, array('97'))) // EXPIRED
	{
		return 'EXPIRED';
	}
	elseif(in_array($sTransactionCode, array('17'))) // CANCELLED
	{
		return 'CANCELLED';
	}

	return 'FAILED';
}
```