Extract slug generator to separate method

The main reason for changing this is that all standard php methods of transliaterationg are unstable (like iconv) or unusable for russian (Transliterator class). So that I managed to extract slug generation to separate method which can be redefined without need to copypaste.

In addition, I created Utils class with static function which applies traditional russian way of transliteration.

I agree that you don't need to return a closure to call it directly after.

Just name the method "transliterate" (or someting) and return this result.
Anyone will be able to replace it in its class anyway. See what I mean?


Otherwise, (and it was the case before already with iconv), but we need to put ext-intl (or ext-iconv) in the list of requires (or suggests) in composer.json IMHO.