Macro containerof::containerof_intrusive

macro_rules! containerof_intrusive {
    ($nt:ident = $container:ty : $field:ident :: $fieldtype:ty) => { ... };
    (pub $nt:ident = $container:ty : $field:ident :: $fieldtype:ty) => { ... };
    (_decl $nt:ident) => { ... };
    (_decl pub $nt:ident) => { ... };
    (_impl $nt:ident = $container:ty : $field:ident :: $fieldtype:ty) => { ... };
}

Define a type representing the translation between an intrusive field and its containing structure.