Logger does not reflect actual listening address and port

When asking Iron to listen on `localhost:0`, the kernel assigns an unused port number, and getaddrinfo resolves localhost to `127.0.0.1`. The actual address can be displayed via `format!("{}", listening.socket)` where `listening` is an instance of the type returned by `Iron::http` and friends.
### Example output from racerd

The first line is my own logging, and the second line is from this crate.

```
racerd listening at 127.0.0.1:54663
GET http://localhost:0/ping -> 200 OK (0.086167 ms)
```
### Discussion

I'm not familiar with all members of the `Request` type, but it seems that Iron would need to pass in either the address or a reference to the listening server in order to access this information.