Add 404 page with trailing slash redirect

404.html

@@ -0,0 +1,19 @@
+---
+layout: default
+title: 404 - Page not found
+---
+
+<div class="page">
+  <h1>Sorry, this page doesn't exist.</h1>
+  <h1>(404 error)</h1>
+</div>
+
+<script>
+  // on 2016-02-01 GitHub Pages upgraded to Jekyll3, which broke all blog posts with trailing slashes
+  // and there are tons of links out there on the web to posts with a trailing slash, so can't ignore it
+  // Fix borrowed from https://github.com/daattali/daattali.github.io/blob/master/404.html#L14-L21
+  var url = location.href;
+  if(url.substr(url.length - 1) === '/') {
+    window.location = url.substr(0, url.length - 1);
+  }
+</script>