Move all examples to their own crates (#201)

This makes it much clearer which dependencies each example has.

examples/tracing-aka-logging/src/main.rs

@@ -0,0 +1,40 @@
+//! Run with
+//!
+//! ```not_rust
+//! cargo run -p example-tracing-aka-logging
+//! ```
+
+use axum::{handler::get, response::Html, route, routing::RoutingDsl};
+use std::net::SocketAddr;
+use tower_http::trace::TraceLayer;
+
+#[tokio::main]
+async fn main() {
+    // Set the RUST_LOG, if it hasn't been explicitly defined
+    if std::env::var("RUST_LOG").is_err() {
+        std::env::set_var(
+            "RUST_LOG",
+            "example_tracing_aka_logging=debug,tower_http=debug",
+        )
+    }
+    tracing_subscriber::fmt::init();
+
+    // build our application with a route
+    let app = route("/", get(handler))
+        // `TraceLayer` is provided by tower-http so you have to add that as a dependency.
+        // It provides good defaults but is also very customizable.
+        // See https://docs.rs/tower-http/0.1.1/tower_http/trace/index.html for more details.
+        .layer(TraceLayer::new_for_http());
+
+    // run it
+    let addr = SocketAddr::from(([127, 0, 0, 1], 3000));
+    tracing::debug!("listening on {}", addr);
+    axum::Server::bind(&addr)
+        .serve(app.into_make_service())
+        .await
+        .unwrap();
+}
+
+async fn handler() -> Html<&'static str> {
+    Html("<h1>Hello, World!</h1>")
+}