New 404 page

templates/404.html

@@ -0,0 +1,8 @@
+{% extends "page.html" %}
+
+{% block main_content %}
+<main class="centered-header">
+  {{ post_macros::page_header(title="404")}}
+  <span>it's not here. i'm sorry.</span>
+</main>
+{% endblock main_content %}