Add automatic self-registration via Composer

[lisachenko]

Autoload can be used for automatic Core initialization, thus simplify usage of this library. Unfortunately, Composer doesn't support automatic preload right now, so only CLI mode can be used for auto-registration right now.

[lisachenko]

Preloading breaks all the things ( Because composer autoloader calls the Core::init() before preload initialization.

[lisachenko]

This issue is also affected by the bug https://bugs.php.net/bug.php?id=78918 which prevents code to be preloaded.