Fixed base64Encoding deprecation, added the actual HTTP status code to connection failure NSError

Fixed base64Encoding deprecation, added the actual HTTP status code to connection failures with key ‘HTTPResponseStatusCode’ in the NSError userInfo dictionary on status codes of >= 400, gives you the ability to see why a connection fails such as a 401 authentication failure
SocketRocket still supports iOS 4 :frowning:  and `-base64EncodedStringWithOptions:` was added in iOS 7, so this should also have a compatibility check around it. Also is there a specific reason you used `NSDataBase64Encoding64CharacterLineLength` instead of the default (`0`)?