Allow using range-based for loops over YamlObject instances by implementing iterators. New YamlObject::DictAdapter and YamlObject::ListAdapter adapter classes are introduced to provide different iterators depending on the object type. Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Reviewed-by: Jacopo Mondi <jacopo@jmondi.org> Reviewed-by: Han-Lin Chen <hanlinchen@chromium.org>