DKIM and Domain Keys class for PHP

The project has moved to GitHub and will not be updated here anymore : https://github.com/louisameline/php-mail-signature

This class is a spin-off of PHPMailer, basically I took only what was necessary for DKIM and improved as much as I could, including with a couple fixes, multiple canonicalization options and the support of Domain Keys. It should be easy as pie to use, check the test file.