Errors coming back from API are not passed on by Request::__call()

[DavidAnderson684]

Using this PHP SDK, I had a customer who was getting back an HTTP 403. That's all the information that could be learned by catching the RuntimeException.

But tinkering inside Request::__call(), I was able to discover that PrintNode was also sending back a useful body:

string(202) "{
  "code": "Forbidden",
  "message": "Your VAT information is inconsistent or incomplete.  Please log in to your account control panel and fix this",
  "uid": "42..."
}

It would be good if that information was obtainable by the consumer, rather than dropped.