An embedded-hal driver for the GP2D12 infrared distance sensor.
Distance calibration is based on the values in the datasheet.
```rust use gp2d12::Gp2d12;
// 3300 mV max voltage on the ADC, 12-bit precision let mut gp2d12 = Gp2d12::new(pin, 3300, 12);
// measuring 40 cm assert_eq!(gp2d12.distance(&mut adc), Ok(Some(40))); ```
See the STM32F3Discovery example for a complete example.