Move all examples to their own crates (#201)

This makes it much clearer which dependencies each example has.

examples/static-file-server/src/main.rs

@@ -0,0 +1,42 @@
+//! Run with
+//!
+//! ```not_rust
+//! cargo run -p example-static-file-server
+//! ```
+
+use axum::{
+    http::StatusCode,
+    routing::{nest, RoutingDsl},
+};
+use std::net::SocketAddr;
+use tower_http::{services::ServeDir, 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_static_file_server=debug,tower_http=debug",
+        )
+    }
+    tracing_subscriber::fmt::init();
+
+    let app = nest(
+        "/static",
+        axum::service::get(ServeDir::new(".")).handle_error(|error: std::io::Error| {
+            Ok::<_, std::convert::Infallible>((
+                StatusCode::INTERNAL_SERVER_ERROR,
+                format!("Unhandled internal error: {}", error),
+            ))
+        }),
+    )
+    .layer(TraceLayer::new_for_http());
+
+    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();
+}