add LED alias for PC13

src/led.rs

@@ -5,6 +5,9 @@
 use stm32f103xx::{GPIOC, RCC};
 
 /// LED connected to pin PC13
+pub type LED = PC13;
+
+/// Pin PC13. There's an LED connected to this pin
 pub struct PC13;
 
 /// Initializes the user LED