Add RTIC example with late resources

As proposed by Mitch in #64. As of this commit, the Teensy CLI loader
does not reject the *.hex file. See the previous commit for details.

examples/rtic_led.rs

@@ -11,38 +11,28 @@
 #![no_std]
 #![no_main]
 
-extern crate panic_halt;
-
-use embedded_hal::digital::v2::OutputPin;
+use embedded_hal::digital::v2::ToggleableOutputPin;
+use panic_halt as _;
 use teensy4_bsp as bsp;
 
-#[rtic::app(device = teensy4_bsp, peripherals = true, monotonic = rtic::cyccnt::CYCCNT)]
+#[rtic::app(device = teensy4_bsp, peripherals = true)]
 const APP: () = {
-    #[init(schedule = [dummy])]
-    fn init(cx: init::Context) {
-        // Cortex-M peripherals
-        let _core = cx.core;
-
-        // Device-specific peripherals
-        let mut device: bsp::Peripherals = cx.device;
-
-        let mut led = bsp::configure_led(&mut device.gpr, device.pins.p13);
-        led.set_high().unwrap();
+    struct Resources {
+        led: bsp::LED,
     }
 
-    #[task]
-    fn dummy(_: dummy::Context) {
-
+    #[init]
+    fn init(mut cx: init::Context) -> init::LateResources {
+        // Prepare the LED.
+        let led = bsp::configure_led(&mut cx.device.gpr, cx.device.pins.p13);
+        init::LateResources { led }
     }
 
-    #[idle]
-    fn idle(_: idle::Context) -> ! {
+    #[idle(resources = [led])]
+    fn idle(cx: idle::Context) -> ! {
+        cx.resources.led.toggle().unwrap();
         loop {
             core::sync::atomic::spin_loop_hint();
         }
     }
-
-    extern "C" {
-        fn LPUART8();
-    }
 };