Better output on exceptions

[dereuromark]

$response->getReasonPhrase() should be included in GithubExceptionThrower

if (400 == $response->getStatusCode()) {
    throw new ErrorException($content['message'], 400);
}

for example just outputs

Problems parsing JSON

But in fact the reason phrase contains the details: reasonPhrase: "Bad Request"
So this should be part of the debugging data IMO.

E.g. as details in brackets:

Problems parsing JSON (Bad Request)

This way I know that this not about the response content, but the actual request.