(fix) latest Iron and Rust

@reem would you mind taking a look? I'm having trouble getting this my examples to compile (so I've removed them here). I keep running into an error message that iron::middleware::ChainBuilder doesn't have any methods in scope named "link", "link_before", or "link_after". It seems to me that these methods ought to be in scope. Thanks!
Since this is a weird middleware that has to be linked both first and last, this should be noted in the docs.

I think dealing with this kind of middleware is a tiny bit unergonomic, and a `Handler -> Handler` abstraction might be needed somewhere.