Macro reproto_backend_doc::define_processor

macro_rules! define_processor {
    ($name:ident, $body:ty, $slf:ident, $($tail:tt)*) => { ... };
    (@tail $slf:ident process => $body:block; $($tail:tt)*) => { ... };
    (@tail $slf:ident current_package => $body:block; $($tail:tt)*) => { ... };
    (@tail $slf:ident current_package => $expr:expr; $($tail:tt)*) => { ... };
    (@tail $slf:ident) => { ... };
}