refactor: adjust createApp related API signatures

BREAKING CHANGE: `createApp` API has been adjusted.

  - `createApp()` now accepts the root component, and optionally a props
  object to pass to the root component.
  - `app.mount()` now accepts a single argument (the root container)
  - `app.unmount()` no longer requires arguments.

  New behavior looks like the following:

  ``` js
  const app = createApp(RootComponent)
  app.mount('#app')
  app.unmount()
  ```

packages/vue/examples/composition/svg.html

@@ -100,7 +100,8 @@ const globalStats = [
   { label: 'E', value: 100 },
   { label: 'F', value: 100 }
 ]
-const App = {
+
+createApp({
   components: {
     Polygraph
   },
@@ -133,9 +134,7 @@ const App = {
       remove
     }
   }
-}
-
-createApp().mount(App, '#demo')
+}).mount('#demo')
 </script>
 
 <style>