Svelte: More idiomatic "emit to parent" (#172)

* Svelte: More idiomatic "emit to parent".

* Run ~~uglier~~ prettier.

* Restore functions.

* Restore `on:event` after merge.

content/4-component-composition/2-emit-to-parent/svelte/AnswerButton.svelte

@@ -1,8 +1,9 @@
 <script>
-  export let onYes;
-  export let onNo;
+  import { createEventDispatcher } from "svelte";
+
+  const dispatch = createEventDispatcher();
 </script>
 
-<button on:click={onYes}> YES </button>
+<button on:click={() => dispatch("yes")}> YES </button>
 
-<button on:click={onNo}> NO </button>
+<button on:click={() => dispatch("no")}> NO </button>

content/4-component-composition/2-emit-to-parent/svelte/App.svelte

@@ -13,5 +13,5 @@
 </script>
 
 <p>Are you happy?</p>
-<AnswerButton onYes={onAnswerYes} onNo={onAnswerNo} />
+<AnswerButton on:yes={onAnswerYes} on:no={onAnswerNo} />
 <p style="font-size: 50px;">{isHappy ? "😀" : "😥"}</p>