atom feed: fix some small issues

src/feed.njk

@@ -14,18 +14,18 @@ metadata:
     id: https://maia.crimew.gay/
 ---
 <?xml version="1.0" encoding="utf-8"?>
-<feed xmlns="http://www.w3.org/2005/Atom">
+<feed xmlns="http://www.w3.org/2005/Atom" xml:base="{{ metadata.url }}">
   <title>{{ metadata.title }}</title>
   <subtitle>{{ metadata.feed.subtitle }}</subtitle>
   <link href="{{ metadata.feed.url }}" rel="self"/>
   <link href="{{ metadata.url }}"/>
-  <updated>{{ collections.posts | rssLastUpdatedDate }}</updated>
+  <updated>{{ collections.posts | getNewestCollectionItemDate | dateToRfc3339 }}</updated>
   <id>{{ metadata.feed.id }}</id>
   <author>
     <name>{{ metadata.author.name }}</name>
     <email>{{ metadata.author.email }}</email>
   </author>
-  {%- for post in collections.posts %}
+  {%- for post in collections.posts | reverse %}
   {% set absolutePostUrl %}{{ post.url | url | absoluteUrl(metadata.url) }}{% endset %}
   <entry>
     <title>{{ post.data.title }}</title>
@@ -34,7 +34,7 @@ metadata:
     {% else %}
       <link href="{{ absolutePostUrl }}"/>
     {% endif %}
-    <updated>{{ post.date | rssDate }}</updated>
+    <updated>{{ post.date | dateToRfc3339 }}</updated>
     <id>{{ absolutePostUrl }}</id>
     <content type="html">{{ post.templateContent | safe | htmlToAbsoluteUrls(absolutePostUrl) }}</content>
   </entry>