Properties
data 
@property (nonatomic, readonly) NSData *data
error
@property (nonatomic, readonly) QBError *error
headers
@property (nonatomic, readonly) NSDictionary *headers
requestUrl
@property (nonatomic, readonly) NSURL *requestUrl
status
@property (nonatomic, readonly) QBResponseStatusCode status
success
@property (nonatomic, getter=isSuccess, readonly) BOOL success
