Add an example of DisplayModel

Based on the earlier example

examples/display_model.rs

@@ -0,0 +1,20 @@
+//! Anything that implements Display can be wrapped in a DisplayModel.
+
+use std::fs::read_dir;
+use std::io;
+use std::thread::sleep;
+use std::time::Duration;
+
+use nutmeg::models::DisplayModel;
+
+fn main() -> io::Result<()> {
+    let options = nutmeg::Options::default();
+    let model = DisplayModel::new(String::new());
+    let view = nutmeg::View::new(model, options);
+    for p in read_dir(".")? {
+        let dir_entry = p?;
+        view.update(|DisplayModel(message)| *message = dir_entry.path().display().to_string());
+        sleep(Duration::from_millis(300));
+    }
+    Ok(())
+}

src/models.rs

@@ -287,6 +287,13 @@ where
 #[derive(Debug)]
 pub struct DisplayModel<T: Display + Debug>(pub T);
 
+impl<T: Display + Debug> DisplayModel<T> {
+    /// Construct a new model holding a value implementing `Display`.
+    pub fn new(value: T) -> DisplayModel<T> {
+        DisplayModel(value)
+    }
+}
+
 impl<T: Display + Debug> Model for DisplayModel<T> {
     fn render(&mut self, _width: usize) -> String {
         format!("{}", self.0)