Added menu functionality. (#58)

* Added core::Channel and menu functionality. core::Channel may leak memory.

* Added leptos example.

examples/leptos/src-tauri/src/main.rs

@@ -0,0 +1,41 @@
+// Prevents additional console window on Windows in release, DO NOT REMOVE!!
+#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")]
+
+use tauri::{Emitter, Manager};
+
+fn main() {
+    logging::enable();
+    tauri::Builder::default()
+        .invoke_handler(tauri::generate_handler![trigger_listen_events,])
+        .run(tauri::generate_context!())
+        .expect("error while running tauri application");
+}
+
+#[tauri::command]
+fn trigger_listen_events(app: tauri::AppHandle) {
+    tracing::debug!("trigger_listen_event");
+    std::thread::spawn({
+        move || {
+            for i in 1..=100 {
+                app.emit("event::listen", i).unwrap();
+                std::thread::sleep(std::time::Duration::from_millis(500));
+            }
+        }
+    });
+}
+
+mod logging {
+    use tracing_subscriber::{filter::LevelFilter, fmt, prelude::*, Layer, Registry};
+
+    const MAX_LOG_LEVEL: LevelFilter = LevelFilter::DEBUG;
+
+    pub fn enable() {
+        let console_logger = fmt::layer()
+            .with_writer(std::io::stdout)
+            .pretty()
+            .with_filter(MAX_LOG_LEVEL);
+
+        let subscriber = Registry::default().with(console_logger);
+        tracing::subscriber::set_global_default(subscriber).unwrap();
+    }
+}