Added rudimentary session based authentication

It has a timeout of 1 minute (still testing!) and is designed to keep
your co-workers and friends out.  As it stands it will not prevent
someone who has access to your server's file system from getting the
credentials, and it will not prevent session based attacks.

You could implement some protection from session fixation rather easily
though by inserting this on line 30... I think...

if (!isset($_SESSION['CREATED'])) {
$_SESSION['CREATED'] = time();
} else if (time() - $_SESSION['CREATED'] > ($session_duration_in_ mins *
60) {
session_regenerate_id(true);
$_SESSION['CREATED'] = time();
}

Next up - "templatitizing" the html for a try at pseudo-MVC in a
standalone script, and making a user editable config section!