Make use of @since comment

I've just found, that @since comment can be used to define a version since when functionality is available. For example:

/**
 * [SCHEDULED TASK] Deletes expired sessions
 *
 * @param kEvent $event
 * @since 5.1.0
 */
function OnDeleteExpiredSessions($event)
{
	if (defined('IS_INSTALL') && IS_INSTALL) {
		return ;
	}
	$this->Application->Session->DeleteExpired();
}

When next time developer will look at that method he can clearly see, that before In-Portal 5.1.0 this method wasn't available.

This would also help, when documentation is generated, because just looking at method comment we can understand if functionality is present in a given version.

To figure out when each of methods/classes is added we need to inspect SVN commit history.