This way there is now only one way to create a router:
```rust
use axum::{Router, handler::get};
let app = Router::new()
.route("/foo", get(handler))
.route("/foo", get(handler));
```
`nest` was changed in the same way:
```rust
use axum::Router;
let app = Router::new().nest("/foo", service);
```
Adds associated `Body` and `BodyError` types to `IntoResponse`. This is required for returning responses with bodies other than `hyper::Body` from handlers. That wasn't previously possible.
This is a breaking change so should be shipped in 0.2.
David Pedersen