Add slider widget

[jrmoulton]

The docs need updated but this works quite well

[jrmoulton]

stack((
    stack((
        widgets::slider::slider(|| 0.)
            .style(|s| {
                s.height(15)
                    .width(200)
                    .set(slider::BarExtends, true)
                    .set(slider::Thickness, 100.pct())
            })
            .on_change_pct(move |val| set_slider.set(val)),
        label(move || format!("Slider value: {:.1}%", get_slider.get() * 100.)),
    ))
    .style(|s| s.gap(5, 0)),
    stack((
        widgets::slider::slider(|| 0.)
            .style(|s| s.height(15).width(200))
            .on_change_pct(move |val| set_slider2.set(val)),
        label(move || format!("Slider value: {:.1}%", get_slider2.get() * 100.)),
    ))
    .style(|s| s.gap(5, 0)),
))
.style(|s| s.flex_col().gap(0, 10)),

Easy to customize

[dzhou121]

Would you mind adding it to the widget-gallery?