Macro derive_model

macro_rules! derive_model {
    (DragDrop for $key:ty) => { ... };
    (Renderer for $key:ty) => { ... };
    (Session for $key:ty) => { ... };
    (Presentation for $key:ty) => { ... };
    ($i:ident, $($is:ident),+ for $key:ty) => { ... };
}