Add example use to IoPin docs

Author: MorganR

src/digital.rs

@@ -176,6 +176,31 @@ pub trait InputPin {
 }
 
 /// Single pin that can switch from input to output mode, and vice-versa.
+/// 
+/// Example use (assumes the Error type is the same for IoPin, InputPin, and
+/// OutputPin):
+/// 
+/// ```
+/// use core::time::Duration;
+/// use embedded_hal::digital::{IoPin, InputPin, OutputPin, PinState};
+/// 
+/// pub fn ping_and_read<TIoPin, TInputPin, TOutputPin, TError>(
+///     pin: TIoPin, delay_fn: &dyn Fn(Duration) -> ()) -> Result<bool, TError>
+/// where TIoPin : IoPin<TInputPin, TOutputPin, Error = TError>,
+///       TInputPin : InputPin<Error = TError> + IoPin<TInputPin, TOutputPin, Error = TError>,
+///       TOutputPin : OutputPin<Error = TError> + IoPin<TInputPin, TOutputPin, Error = TError> {
+/// 
+///     // Ping
+///     let mut pin = pin.try_into_output_pin(PinState::Low)?;
+///     delay_fn(Duration::from_millis(10));
+///     pin.try_set_high()?;
+/// 
+///     // Read
+///     let pin = pin.try_into_input_pin()?;
+///     delay_fn(Duration::from_millis(10));
+///     pin.try_is_high()
+/// }
+/// ```
 pub trait IoPin<TInput, TOutput> 
 where TInput : InputPin + IoPin<TInput, TOutput>,
       TOutput : OutputPin + IoPin<TInput, TOutput> {