Add default layout that doesn't override the head

docs/rollup.config.js

@@ -38,6 +38,7 @@ const preprocess = [
   mdsvex({
     layout: {
       docs: './src/mdsvex/layout.svelte',
+      _: './src/mdsvex/layout-no-head.svelte',
     },
     smartypants: {
       quotes: false,

docs/src/mdsvex/layout-no-head.svelte

@@ -0,0 +1,29 @@
+<script context="module">
+  import Heading1 from 'src/mdsvex/h1.svelte';
+  import Heading2 from 'src/mdsvex/h2.svelte';
+  import Heading3 from 'src/mdsvex/h3.svelte';
+  import UnorderedList from 'src/mdsvex/ul.svelte';
+  import ListItem from 'src/mdsvex/li.svelte';
+  import Table from 'src/mdsvex/table.svelte';
+  import TableHead from 'src/mdsvex/th.svelte';
+  import TableRow from 'src/mdsvex/tr.svelte';
+  import TableData from 'src/mdsvex/td.svelte';
+  import Mark from 'src/mdsvex/mark.svelte';
+  import Paragraph from 'src/mdsvex/p.svelte';
+
+  export {
+    Heading1 as h1,
+    Heading2 as h2,
+    Heading3 as h3,
+    UnorderedList as ul,
+    ListItem as li,
+    Table as table,
+    TableHead as th,
+    TableRow as tr,
+    TableData as td,
+    Mark as mark,
+    Paragraph as p,
+  };
+</script>
+
+<slot />