* Refactor initializing tracing-subscriber
* Revert "Refactor initializing tracing-subscriber"
This reverts commit 0876260bf9 in favor of tracing_subscriber::registry.
* Use EnvFilter::try_from_default_env in chat example
* Use EnvFilter::try_from_default_env in examples
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);
```
