examples: Consistently use unwrap! in favor of .unwrap()

Unfortunately errors from `embedded_graphics` and `core` doesn't provide
the necessary instances currently.

examples/stm32l4/src/bin/button.rs

@@ -24,7 +24,7 @@ fn main() -> ! {
     let button = Input::new(p.PC13, Pull::Up);
 
     loop {
-        if button.is_high().unwrap() {
+        if unwrap!(button.is_high()) {
             info!("high");
         } else {
             info!("low");