(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!
Separate issue, but looking through the formatting code it occurs to me that this does a lot of unnecessary copies and allocations relating to misuse of `String`.