Support being mounted on a path — fixes #180

test/app/routes/blog/index.html

@@ -11,7 +11,7 @@
 			     tell Sapper to load the data for the page as soon as
 			     the user hovers over the link or taps it, instead of
 			     waiting for the 'click' event -->
-			<li><a rel='prefetch' href='/blog/{{post.slug}}'>{{post.title}}</a></li>
+			<li><a rel='prefetch' href='blog/{{post.slug}}'>{{post.title}}</a></li>
 		{{/each}}
 	</ul>
 </Layout>
@@ -32,7 +32,7 @@
 		},
 
 		preload({ params, query }) {
-			return fetch(`/blog.json`).then(r => r.json()).then(posts => {
+			return fetch(`blog.json`).then(r => r.json()).then(posts => {
 				return { posts };
 			});
 		}