Allow overriding guzzle options in Transport object
Allow overriding guzzle options in Transport object

This then allows me to override like this:

```php
        $connection = new Transport($url, $params['username'], $params['password'], [
            'defaults'=> array(
                'headers' => array(
                    'Accept' => 'application/json',
                ),
                'auth' => [$params['username'], $params['password']]
            )
        ]);
        $this->targetprocess = new Client($connection);
```

Overriding the 'auth' config option, so it works for me (without breaking your existing version)! :-)
toecto/targetprocess-php-client