Introduce a Signal class that allows connecting event sources (signals) to event listeners (slots) without adding any boilerplate code usually associated with the observer or listener design patterns. Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se> Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>