Macro delegate_impl

macro_rules! delegate_impl {
    ([] $($rest:tt)*) => { ... };
    ([[$($param:tt)*], $self_type:ident, $self_wrap:ty, $self_map:ident]
     pub trait $name:ident $(: $sup:ident)* $(+ $more_sup:ident)* {

        // "Escaped" associated types. Stripped before making the `trait`
        // itself, but forwarded when delegating impls.
        $(
        @escape [type $assoc_name_ext:ident]
        // Associated types. Forwarded.
        )*
        $(
        @section type
        $(
            $(#[$_assoc_attr:meta])*
            type $assoc_name:ident $(: $assoc_bound:ty)*;
        )+
        )*
        // Methods. Forwarded. Using $self_map!(self) around the self argument.
        // Methods must use receiver `self` or explicit type like `self: &Self`
        // &self and &mut self are _not_ supported.
        $(
        @section self
        $(
            $(#[$_method_attr:meta])*
            fn $method_name:ident(self $(: $self_selftype:ty)* $(,$marg:ident : $marg_ty:ty)*) -> $mret:ty;
        )+
        )*
        // Arbitrary tail that is ignored when forwarding.
        $(
        @section nodelegate
        $($tail:tt)*
        )*
    }) => { ... };
}

Implement a trait by delegation. By default as if we are delegating from &G to G.