Add toggle

examples/signals.rs

@@ -23,7 +23,7 @@ fn app(cx: Scope) -> Element {
         h1 { "High-Five counter: {count}" }
         button { onclick: move |_| count += 1, "Up high!" }
         button { onclick: move |_| count -= 1, "Down low!" }
-        button { onclick: move |_| running.set(!running.value()), "Toggle counter" }
+        button { onclick: move |_| running.toggle(), "Toggle counter" }
         button { onclick: move |_| saved_values.push(count.value()), "Save this value" }
 
         // We can do boolean operations on the current signal value