Add minimal example, some formatting, bump parking_lot version

examples/minimal/main.rs

@@ -0,0 +1,28 @@
+#[macro_use]
+extern crate rocket;
+
+use std::time::Duration;
+
+type Session<'a> = rocket_session::Session<'a, u64>;
+
+#[launch]
+fn rocket() -> _ {
+    // This session expires in 15 seconds as a demonstration of session configuration
+    rocket::build()
+        .attach(Session::fairing().with_lifetime(Duration::from_secs(15)))
+        .mount("/", routes![index])
+}
+
+#[get("/")]
+fn index(session: Session) -> String {
+    let count = session.tap(|n| {
+        // Change the stored value (it is &mut)
+        *n += 1;
+
+        // Return something to the caller.
+        // This can be any type, 'tap' is generic.
+        *n
+    });
+
+    format!("{} visits", count)
+}