Pass $ext, $payload, and $contentType into generateHawkRequest from signRequest

[alxmrtn]

generateHawkRequest() accepts 8 parameters with the last 3 being $ext, $payload and $contentType. signRequest() currently does not pass these 3 values into generateHawkRequest()

[jeskew]

signRequest() will be called directly by Guzzle and isn't really a userland function. Would it make sense to instead pass a $parsePayload directive into the constructor that would tell $signRequest to get those values from the request?

[jeskew]

Would this be fixed by #3 ?