Draft TextInput widget structure

Also started a `todos` example to showcase it!

examples/todos.rs

@@ -0,0 +1,69 @@
+use iced::{
+    text::HorizontalAlignment, text_input, Align, Application, Color, Column,
+    Element, Justify, Length, Text, TextInput,
+};
+
+pub fn main() {
+    Todos::default().run()
+}
+
+#[derive(Default)]
+struct Todos {
+    input: text_input::State,
+    input_value: String,
+}
+
+#[derive(Debug, Clone)]
+pub enum Message {
+    InputChanged(String),
+    CreateTask,
+}
+
+impl Application for Todos {
+    type Message = Message;
+
+    fn update(&mut self, message: Message) {
+        match message {
+            Message::InputChanged(value) => {
+                self.input_value = value;
+            }
+            Message::CreateTask => {}
+        }
+    }
+
+    fn view(&mut self) -> Element<Message> {
+        let title = Text::new("todos")
+            .size(100)
+            .color(GRAY)
+            .horizontal_alignment(HorizontalAlignment::Center);
+
+        let input = TextInput::new(
+            &mut self.input,
+            "What needs to be done?",
+            &self.input_value,
+            Message::InputChanged,
+        )
+        .padding(15)
+        .size(30)
+        .on_submit(Message::CreateTask);
+
+        Column::new()
+            .max_width(Length::Units(800))
+            .height(Length::Fill)
+            .align_self(Align::Center)
+            .justify_content(Justify::Center)
+            .spacing(20)
+            .padding(20)
+            .push(title)
+            .push(input)
+            .into()
+    }
+}
+
+// Colors
+const GRAY: Color = Color {
+    r: 0.5,
+    g: 0.5,
+    b: 0.5,
+    a: 1.0,
+};