Make Str:ascii use character translit map

Ok, alternative String class rewrite.

Works the same way as Str class except for transliteration it uses more reliable character map array.

Also one small feature is a language priority (third argument in slug/second argument in ascii).

Should be used in order to specify which language has priority during transliteration.

For example:

* Str::ascii('ö') => 'o'
* Str::ascii('ö','de') => 'oe'