Replace 404.md with a 404.html template

blog/content/pages/404.md

@@ -1,13 +0,0 @@
-+++
-title = "Page not found"
-path = "404.html"
-template = "plain.html"
-+++
-
-Sorry, we've misplaced that URL or it's pointing to something that doesn't exist.
-
-[Head back home](/) to try finding it again.
-
-If you followed a link on this site, please [report it]!
-
-[report it]: https://github.com/phil-opp/blog_os/issues

blog/templates/404.html

@@ -0,0 +1,12 @@
+{% extends "second-edition/base.html" %}
+
+{% block title %}Page not found | {{ config.title }}{% endblock title %}
+
+{% block main %}
+    <h1>Page not found</h1>
+    <p>Sorry, this address is not valid.</p>
+
+    <p><a href="{{ config.base_url }}">Go to the index page</a>.</p>
+
+    <p>If you followed a link on this site, please <a href="https://github.com/phil-opp/blog_os/issues">report it</a>!</p>
+{% endblock main %}

blog/templates/second-edition/base.html

@@ -9,7 +9,9 @@
     <meta name="description" content="{{ config.description }}">
     <meta name="author" content="{{ config.extra.author.name }}">
 
+    {% if current_url %}
         <link rel="canonical" href="{{ current_url | safe }}" />
+    {% endif %}
     <link href="/css/poole.css" rel="stylesheet">
     <link href="/css/main.css" rel="stylesheet">