Abstract boards

[conorpp]

Added traits and abstractions for LED and buttons for both Xpresso and Bee boards. Haven't committed to lib.rs or app_rtfm.rs yet, but locally I'm using them like so.

    #[cfg(feature = "board-lpcxpresso")]
    let rgb = board::led::Rgb::new(
        board::led::RedLedPin::take().unwrap().into_match_output(&mut iocon),
        board::led::GreenLedPin::take().unwrap().into_match_output(&mut iocon),
        board::led::BlueLedPin::take().unwrap().into_match_output(&mut iocon),
        Pwm::new(hal.ctimer.2.enabled(&mut syscon)),
    );

    #[cfg(feature = "board-prototype")]
    let rgb = board::led::Rgb::new(
        board::led::RedLedPin::take().unwrap().into_match_output(&mut iocon),
        board::led::GreenLedPin::take().unwrap().into_match_output(&mut iocon),
        board::led::BlueLedPin::take().unwrap().into_match_output(&mut iocon),
        Pwm::new(hal.ctimer.3.enabled(&mut syscon)),
    );

    #[cfg(feature = "board-lpcxpresso")]
    let three_buttons = board::button::ThreeButtons::new(
        Timer::new(hal.ctimer.1.enabled(&mut syscon)),
        board::button::UserButtonPin::take().unwrap().into_gpio_pin(&mut iocon, &mut gpio).into_input(),
        board::button::WakeupButtonPin::take().unwrap().into_gpio_pin(&mut iocon, &mut gpio).into_input(),
    );


    #[cfg(feature = "board-prototype")]
    let three_buttons =
    {
        let mut dma = hal::Dma::from(hal.dma).enabled(&mut syscon);

        board::button::ThreeButtons::new (
            hal::Adc::from(hal.adc).enabled(&mut pmc, &mut syscon),
            hal.ctimer.1.enabled(&mut syscon),
            hal.ctimer.2.enabled(&mut syscon),
            board::button::ChargeMatchPin::take().unwrap().into_match_output(&mut iocon),
            board::button::ButtonTopPin::take().unwrap().into_analog_input(&mut iocon, &mut gpio),
            board::button::ButtonBotPin::take().unwrap().into_analog_input(&mut iocon, &mut gpio),
            board::button::ButtonMidPin::take().unwrap().into_analog_input(&mut iocon, &mut gpio),
            &mut dma,
            clocks.support_touch_token().unwrap(),
        )
    };

I've had to make minor changes to the HAL, so this will depend on another HAL release.