ClientException does not provide error code as integer

[kmbt]

REST-API/src/FreshMail/Client.php

Line 77 in 053b7ec

throw new \FreshMail\ApiV2\ClientException(sprintf('Connection error, error message: '.$exception->getMessage()));

\FreshMail\ApiV2\ClientException only holds a message such as:

Connection error, error message: Client error: `POST https://api.freshmail.com/rest/subscriber/add` resulted in a `422 Unprocessable Entity` response:
{"status":"ERROR","errors":[{"message":"Subscribers already exists in this subscribers list","code":1304}]}

This is not much use for handling this exception in code, as the exception code 1304 is not directly provided on the \FreshMail\ApiV2\ClientException object. It is only a part of the message string.

It would be tremendously useful if the code was easily accessible on the exception object as simple integer.

[fugi]

I propose a PR #19