Add: docs for event extension

git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@329773 c90b9560-bf6c-de11-be94-00142212c4b1
Refact: applied xml formatting

git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@329774 c90b9560-bf6c-de11-be94-00142212c4b1