add(widget): primitive progressbar widget

examples/progressbar.rs

@@ -0,0 +1,51 @@
+use iced::{slider, Column, Element, Sandbox, Settings, Slider};
+use iced_winit::Progressbar;
+
+pub fn main() {
+    Progress::run(Settings::default())
+}
+
+#[derive(Default)]
+struct Progress {
+    value: f32,
+    progressbar_slider: slider::State,
+}
+
+#[derive(Debug, Clone, Copy)]
+enum Message {
+    SliderChanged(f32),
+}
+
+impl Sandbox for Progress {
+    type Message = Message;
+
+    fn new() -> Self {
+        Self::default()
+    }
+
+    fn title(&self) -> String {
+        String::from("A simple Progressbar")
+    }
+
+    fn update(&mut self, message: Message) {
+        match message {
+            Message::SliderChanged(x) => {
+                self.value = x;
+            }
+        }
+    }
+
+    fn view(&mut self) -> Element<Message> {
+        Column::new()
+            .padding(20)
+            .push(Progressbar::new(0.0..=100.0, self.value))
+            .padding(20)
+            .push(Slider::new(
+                &mut self.progressbar_slider,
+                0.0..=100.0,
+                self.value,
+                Message::SliderChanged,
+            ))
+            .into()
+    }
+}