added email confirmation to the DBAuthMiddleware using phpmailer.

[aleppax]

added documentation.
some new configuration settings are required and I've grouped those related to the SMTP settings into an array. see the documentation. First version, may have errors. Tested only with my installation.

[aleppax]

I'm not satisfied with the

require 'vendor/phpmailer/phpmailer/src/Exception.php';
require 'vendor/phpmailer/phpmailer/src/PHPMailer.php';
require 'vendor/phpmailer/phpmailer/src/SMTP.php';

because if the script api.php or the files are in a different path the server returns a 500 error