* Replace a couple of methods with native functions (Max Semenik)
  * Utils::codepointToUtf8() is deprecated in favor of mb_chr()
  * Utils::utf8ToCodepoint() is deprecated in favor of mb_ord()
* Require mbstring PHP extension (Kunal Mehta)
* Drop support for PHP < 7.2, HHVM (James D. Forrester)
* Mark all constants as public (Reedy)