Macro gstore::widget

macro_rules! widget {
    (
        $widget:ident {
            $(class $class:literal)?
            $(properties $($stateful:ident)? {
                $( $prop:ident: $value:expr )*
            })?
            $(connecting $store:ident {
                $($connector:ident: $connection:expr)*
            })?
            $(children [
                $($child:expr)*
            ])?
        }
    ) => { ... };
}