TransactionAmount parameter uses complex type

Referencing the AWS documentation for the `Pay` operation: http://docs.aws.amazon.com/AmazonFPS/latest/FPSAPIReference/Pay.html

The `TransactionAmount` parameter uses the complex type defined here: http://docs.aws.amazon.com/AmazonFPS/latest/FPSAPIReference/Amount.html

The example request shows this formatted like so:

```
https://fps.sandbox.amazonaws.com?
Action=Pay
&AWSAccessKeyId=AKIAIOSFODNN7EXAMPLE
&CallerDescription=MyWish
&CallerReference=CallerReference02
&SenderTokenId=553ILMLCG6Z8J431H7BX3UMN3FFQU8VSNTSRNCTAASDJNX66LNZLKSZU3PI7TXIH
&Signature=0AgvXMwJmLxwdMaiE7lMHZxc6384h%2FjBkiTserQFpBQ%3D
&SignatureMethod=HmacSHA256
&SignatureVersion=2
&Timestamp=2009-10-06T05%3A49%3A52.843Z
&TransactionAmount.CurrencyCode=USD
&TransactionAmount.Value=1
&Version=2008-09-17
```

This updates the configuration for the Pay operation to send the properly formatted complex type. I found this after receiving this odd message back from AWS, using just `TransactionStatus`:

```
<Response>
    <Errors>
        <Error>
            <Code>InvalidParams</Code>
            <Message>transactionAmount.amount can not be null</Message>
        </Error>
    </Errors>
    <RequestID>b1310d92-c743-4ff4-871f-070becd766b5</RequestID>
</Response>
```

After this change I began receiving a proper response.