Macro vobject

macro_rules! vobject {
    ($name:ident $($tokens:tt)*) => { ... };
    (($name:expr) $($tokens:tt)*) => { ... };
    () => { ... };
    (~private $items:path | $name:ident $($tokens:tt)*) => { ... };
    (~private $items:path | ($name:expr) : $value:expr , $($excess:tt)*) => { ... };
    (~private $items:path | ($name:expr) : $value:expr) => { ... };
    (~private $items:path |) => { ... };
}

Helper macro for constructing Value objects. Object body is similar to a Rust struct body, and field values are automatically converted to Value via the From trait.