Support Svelte 3

fixes #546, #551, #552, #554

test/apps/export/src/routes/blog/[slug].html

@@ -1,11 +1,13 @@
-<h1>{post.title}</h1>
+<script context="module">
+	export function preload({ params }) {
+		return this.fetch(`blog/${params.slug}.json`).then(r => r.json()).then(post => {
+			return { post };
+		});
+	}
+</script>
 
 <script>
-	export default {
-		preload({ params }) {
-			return this.fetch(`blog/${params.slug}.json`).then(r => r.json()).then(post => {
-				return { post };
-			});
-		}
-	};
-</script>
+	export let post;
+</script>
+
+<h1>{post.title}</h1>

test/apps/export/src/routes/blog/index.html

@@ -1,15 +1,17 @@
+<script context="module">
+	export function preload() {
+		return this.fetch('blog.json').then(r => r.json()).then(posts => {
+			return { posts };
+		});
+	}
+</script>
+
+<script>
+	export let posts;
+</script>
+
 <h1>blog</h1>
 
 {#each posts as post}
 	<p><a href="blog/{post.slug}">{post.title}</a></p>
-{/each}
-
-<script>
-	export default {
-		preload() {
-			return this.fetch('blog.json').then(r => r.json()).then(posts => {
-				return { posts };
-			});
-		}
-	};
-</script>
+{/each}