[+]: add "Portable UTF-8"

One more string manipulation library, with UTF-8 safe replacement methods.

-> https://github.com/voku/portable-utf8#class-methods

README.md

 * [Jieba-PHP](https://github.com/fukuball/jieba-php) - A PHP port of Python's jieba. Chinese text segmentation for natural language processing.
 * [Mobile-Detect](https://github.com/serbanghita/Mobile-Detect) - A lightweight PHP class for detecting mobile devices (including tablets).
 * [Patchwork UTF-8](https://github.com/nicolas-grekas/Patchwork-UTF8) - A portable library for working with UTF-8 strings.
+* [Portable UTF-8](https://github.com/voku/portable-utf8) - A string manipulation library with UTF-8 safe replacement methods.
 * [Slugify](https://github.com/cocur/slugify) - A library to convert strings to slugs.
 * [SQL Formatter](https://github.com/jdorn/sql-formatter/) - A library for formatting SQL statements.
 * [Stringy](https://github.com/danielstjules/Stringy) - A string manipulation library with multibyte support.