Convert callUserMethod & parseGetResponse from `private` to `protected` to allow using when extending the methods

Hi @fehrlich,

I was trying to implement a new Method the get all real estate Objects from is24.

I followed your code in the getContacts method & did the same.

but I ran into an Error Uncaught Error: Argument 2 passed to GuzzleHttp\Command\Guzzle\GuzzleClient::getCommand().

after I checked the code, turns out that the callUserMethod & parseGetResponse are private methods & I can not use them.

so would you mind changing the visibility of this methods from private to protected and allowing me to use them ?

Best Regards Omar