XZ Utils wrapper for #PHP

I took a liking to the xz compression format a long time ago. It is a very handy format that is available almost everywhere, unfortunately not in PHP. So I decided it is time to fix that and write an XZ Utils (wrapper).

It is a simple piece of code that can be used either:

• PHP-usually, through functions that return a falsable string, xzencode('my uncompressed data'),
• or normally, with strict typing and exceptions, (new Xz())->compress('my uncompressed data').

You’re welcome, have fun. :)