(cleanup) Tidy rust-url usage, restore old API.

I've tidied up the use of `unwrap` on URL data. The `rust-url` library provides a number of useful guarantees. See: https://github.com/iron/static-file/pull/28.

Not sure if you want to keep the API change I made? Is `&[&str]` for routes preferred over `&str`? I figure using `Path` is ok, but haven't looked into Windows compatibility...

Don't merge yet, untested due to `Share` -> `Sync` problem in `rust-encoding`. Waiting on https://github.com/lifthrasiir/rust-encoding/issues/34.