Added menu functionality. (#58)

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

* Added leptos example.

examples/leptos/Cargo.toml

@@ -0,0 +1,22 @@
+[package]
+name = "test-tauri-events-ui"
+version = "0.0.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+[dependencies]
+leptos = { version = "0.6", features = ["csr", "nightly"] }
+wasm-bindgen = "0.2"
+wasm-bindgen-futures = "0.4"
+js-sys = "0.3"
+serde = { version = "1", features = ["derive"] }
+serde-wasm-bindgen = "0.6"
+console_error_panic_hook = "0.1.7"
+tauri-sys = { path = "../tauri-sys", features = ["all"] }
+futures = "0.3"
+tracing = "0.1.40"
+tracing-subscriber = "0.3.18"
+tracing-web = "0.1.3"
+
+[workspace]
+members = ["src-tauri"]