Add futures-tokio-basic example (not working yet)

There's some issues with the example right now. See
https://github.com/Meziu/ctru-rs/pull/36#issuecomment-1028617954

ctru-rs/Cargo.toml

@@ -26,6 +26,7 @@ toml = "0.5"
 [dev-dependencies]
 ferris-says = "0.2.1"
 time = "0.3.7"
+tokio = { version = "1.16", features = ["rt", "time", "sync", "macros"] }
 
 [features]
 default = ["romfs"]

ctru-rs/examples/futures-tokio-basic.rs

@@ -0,0 +1,65 @@
+use ctru::console::Console;
+use ctru::services::hid::KeyPad;
+use ctru::services::{Apt, Hid};
+use ctru::Gfx;
+use std::time::Duration;
+
+fn main() {
+    ctru::init();
+    let gfx = Gfx::default();
+    let hid = Hid::init().expect("Couldn't obtain HID controller");
+    let apt = Apt::init().expect("Couldn't obtain APT controller");
+    let _console = Console::init(gfx.top_screen.borrow_mut());
+
+    // FIXME: replace this with `Ps` when #39 merges
+    assert!(unsafe { ctru_sys::psInit() } >= 0);
+
+    // Give ourselves up to 30% of the system core's time
+    apt.set_app_cpu_time_limit(30)
+        .expect("Failed to enable system core");
+
+    println!("Starting runtime...");
+
+    let (exit_sender, mut exit_receiver) = tokio::sync::oneshot::channel();
+    let runtime = tokio::runtime::Builder::new_current_thread()
+        .enable_time()
+        .build()
+        .expect("Couldn't build runtime");
+
+    let runtime_thread = ctru::thread::Builder::new()
+        .affinity(1)
+        .spawn(move || {
+            runtime.block_on(async move {
+                let mut wake_time = tokio::time::Instant::now() + Duration::from_secs(1);
+                loop {
+                    let sleep_future = tokio::time::sleep_until(wake_time);
+
+                    tokio::select! {
+                        _ = &mut exit_receiver => break,
+                        _ = sleep_future => {
+                            println!("Tick");
+                            wake_time += Duration::from_secs(1);
+                        }
+                    }
+                }
+            });
+        })
+        .expect("Failed to create runtime thread");
+
+    println!("Runtime started!");
+
+    while apt.main_loop() {
+        hid.scan_input();
+
+        if hid.keys_down().contains(KeyPad::KEY_START) {
+            println!("Shutting down...");
+            let _ = exit_sender.send(());
+            let _ = runtime_thread.join();
+            break;
+        }
+
+        gfx.flush_buffers();
+        gfx.swap_buffers();
+        gfx.wait_for_vblank();
+    }
+}