//! Digital I/O
/// Single digital push-pull output pin
/// Push-pull output pin that can read its output state
/// Output pin that can be toggled
///
/// See [toggleable](toggleable) to use a software implementation if
/// both [OutputPin](trait.OutputPin.html) and
/// [StatefulOutputPin](trait.StatefulOutputPin.html) are
/// implemented. Otherwise, implement this using hardware mechanisms.
/// If you can read **and** write the output state, a pin is
/// toggleable by software.
///
/// ```
/// use embedded_hal::digital::{OutputPin, StatefulOutputPin, ToggleableOutputPin};
/// use embedded_hal::digital::toggleable;
///
/// /// A virtual output pin that exists purely in software
/// struct MyPin {
/// state: bool
/// }
///
/// impl OutputPin for MyPin {
/// fn set_low(&mut self) {
/// self.state = false;
/// }
/// fn set_high(&mut self) {
/// self.state = true;
/// }
/// }
///
/// impl StatefulOutputPin for MyPin {
/// fn is_set_low(&self) -> bool {
/// !self.state
/// }
/// fn is_set_high(&self) -> bool {
/// self.state
/// }
/// }
///
/// /// Opt-in to the software implementation.
/// impl toggleable::Default for MyPin {}
///
/// let mut pin = MyPin { state: false };
/// pin.toggle();
/// assert!(pin.is_set_high());
/// pin.toggle();
/// assert!(pin.is_set_low());
/// ```
/// Single digital input pin