This removes a small foot gun from the routing.
This means matching different HTTP methods for the same route that
aren't defined together now works.
So `Router::new().route("/", get(...)).route("/", post(...))` now
accepts both `GET` and `POST`. Previously only `POST` would be accepted.
With this you'll be able to do:
```rust
let one = route("/foo", get(|| async { "foo" }))
.route("/bar", get(|| async { "bar" }));
let two = route("/baz", get(|| async { "baz" }));
let app = one.or(two);
```
Fixes https://github.com/tokio-rs/axum/issues/101
David Pedersen