Improve blog setup

- Use post title in banner.
- Add native.css for testing syntax highlighting.

src/routes/blog/[slug].svelte

@@ -58,10 +58,9 @@
     <title>{post.title}</title>
 </svelte:head>
 
-<Banner/>
+<Banner title={post.title}/>
 
 <main class="container">
-    <h1>{post.title}</h1>
     <section>
         {@html post.html}
     </section>

src/routes/blog/_posts.js

@@ -34,7 +34,7 @@ const posts = [
 			<h2>Step one</h2>
 			<p>Create a new project, using <a href='https://github.com/Rich-Harris/degit'>degit</a>:</p>
 
-			<pre><code>npx degit "sveltejs/sapper-template#rollup" my-app
+			<pre class="highlight"><code>npx degit "sveltejs/sapper-template#rollup" my-app
 			cd my-app
 			npm install # or yarn!
 			npm run dev