Add proc macro to derive pins and component

[jamwaffles]

Similar to the HAL component generator, a proc macro to set up pins, signals and the component would be super kool. Something like:

struct ThingState {
    // Whatever
}

#[derive(halcomp)]
#[halcomp("comp-name")]
pub struct MyComponent {
    #[halcomp(pin = "float-input", input)]
    some_float_input: f32,

    #[halcomp(pin = "a-flag", input)]
    some_flag: bool,

    #[halcomp(pin = "tell-lcnc-about-this", output)]
    out_value: u32,

    /// Some internal value to the component
    something_inside: ThingState
}