Replaced deprecated /e flag with preg_replace_callback

See the following link with information on why it is deprecated:
http://php.net/manual/en/reference.pcre.pattern.modifiers.php#reference.pcre.pattern.modifiers.eval
Merge pull request #63 from Tenzer/preg_replace-php_5.5_fix

Replaced deprecated preg_replace /e flag with preg_replace_callback