Replace route with Router::new().route() (#215)

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);
```

examples/tokio-postgres/src/main.rs

@@ -9,7 +9,7 @@ use axum::{
     extract::{Extension, FromRequest, RequestParts},
     handler::get,
     http::StatusCode,
-    route, AddExtensionLayer,
+    AddExtensionLayer, Router,
 };
 use bb8::{Pool, PooledConnection};
 use bb8_postgres::PostgresConnectionManager;
@@ -31,11 +31,12 @@ async fn main() {
     let pool = Pool::builder().build(manager).await.unwrap();
 
     // build our application with some routes
-    let app = route(
-        "/",
-        get(using_connection_pool_extractor).post(using_connection_extractor),
-    )
-    .layer(AddExtensionLayer::new(pool));
+    let app = Router::new()
+        .route(
+            "/",
+            get(using_connection_pool_extractor).post(using_connection_extractor),
+        )
+        .layer(AddExtensionLayer::new(pool));
 
     // run it with hyper
     let addr = SocketAddr::from(([127, 0, 0, 1], 3000));