Hello world example and confirming the script works with 151S AVR

[felagund]

Thank you for the library. It works with my 151S AVR model.

I have never used php before so it took me a bit to set it up, my streamlined notes on a Ubuntu/Debian are below. My use case was to be able to use a script to turn the AVR off when I turn my Raspberry Pi off automatically. This accomplishes it:

1. Install the composer dependency manager (for Debian/Ubuntu):
   sudo apt install composer
2. Create a working directory somewhere:
   mkdir my_avr_script ; cd my_avr_script
3. Create a composer.json file in your working directory with this content:

{
    "require-dev": {
    "karimgeiger/hkapi": "1.0.x-dev"
}
}

4. Install the library with:
   composer update ; composer install
5. Create an example script turn_off.php with this content:

<?php require __DIR__ . '/vendor/autoload.php'; 
echo "Hello World!'\n";
$hk = new \HKAPI\API('192.168.2.206',10025, new \HKAPI\Devices\AVR());
sleep(3);
$hk->zone('Main Zone')->off();
?>

6. Turn your AVR off with:
   php turn_off.php

It should output:

Hello World!
PHP Notice:  Undefined offset: 0 in /home/pi/skripty_na_AVR/vendor/karimgeiger/hkapi/lib/Zone.php on line 95

(the first confirms the script ran and the second is a PHP warning that can be safely ignored it seems)
and the AVR should turn off after three seconds.

[felagund]

@KarimGeiger I noticed in other issues you do not get notifications so here I am trying to send you one.

Also, I have a question - any idea how one could turn the device off instead of putting it to sleep? Becasue putting it to sleep is what $hk->zone('Main Zone')->off(); does.