Add settings

[usbalbin]

Solves #8

Adds settings. Just like Metrics, Settings are detected by probe-plotter-tools, however instead of being plotted the program adds sliders(see top right corner). When the sliders are changed, the value is sent to the MCU

fn init(...) {
    // make_setting!(VAR_NAME: Type = default, min_value..=max_value, step_size)
    let mut duty = make_setting!(DUTY: u16 = 10, 10..=90, 10).unwrap();

    // duty is constrained to 10..=90% and is set in increments of 10

    let pwm = setup_some_pwm_thing();
}

fn update(...) {
    pwm.set_duty(duty.get()); // Get the latest value as set by probe-plotter-tools
}

Other example from README.md:

---

Note This PR changes the expression syntax for the make_metric macro. Do not use x to refer to the value, instead use the assigned name like so:

let mut sawtooth = make_metric!(SAWTOOTH: i32 = 42, "(SAWTOOTH / 10) % 100").unwrap();

[usbalbin]

@AdinAck Any thoughts on the settings feature?

[AdinAck]

@AdinAck Any thoughts on the settings feature?

Oh nice, I didn't even know rerun had that!

[usbalbin]

@AdinAck Any thoughts on the settings feature?

Oh nice, I didn't even know rerun had that!

It does not. But since rerun is built using egui it was quite simple to just add a panel for the settings