php中有什么比较好的文本库，可以比对一篇文章的两个版本修改了哪些内容。
https://github.com/chrisboulton/php-diff
http://paulbutler.org/archives/a-simple-diff-algorithm-in-php/
http://php.net/manual/en/function.similar-text.php
http://php.net/manual/en/function.levenshtein.php
http://php.net/manual/en/function.soundex.php
http://php.net/manual/en/function.metaphone.php
http://php.net/manual/en/book.xdiff.php
http://pear.php.net/package/Text_Diff