defining first Display and Registry structs. Added Callback support for Registry.

examples/simple_client.rs

@@ -0,0 +1,17 @@
+// SPDX-License-Identifer: GPL-2.0-only
+
+use std::io;
+
+use wayland_client::display::Display;
+
+fn main() -> io::Result<()> {
+    let display = Display::new(None)?;
+    println!("Connection established!");
+
+    while let Some(_events) = display.dispatch() {
+
+    }
+
+    drop(display);
+    Ok(())
+}