rebuild code based on callbacks instead of an interface and an abstract class
+ added "unsecure" link for testing purpose
redirection page can now be configured in constructor
updated README to fit new architecture
keep $login and $sid separated in callbacks (instead of using $cookieValue = $login.'_'.$sid)
minor fixes
- only start PHP session if needed
- only unset session values if they exist
- exit after redirections
- only log data if not empty (superglobals and variables)