Improve feed.xml.

feed.xml

@@ -1,13 +1,23 @@
 ---
-layout: none
+layout: nil
 ---
-<?xml version="1.0" encoding="UTF-8"?>
-<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">
+<?xml version="1.0" encoding="utf-8"?>
+<rss version="2.0"
+  xmlns:content="http://purl.org/rss/1.0/modules/content/"
+  xmlns:wfw="http://wellformedweb.org/CommentAPI/"
+  xmlns:dc="http://purl.org/dc/elements/1.1/"
+  xmlns:atom="http://www.w3.org/2005/Atom"
+  xmlns:sy="http://purl.org/rss/1.0/modules/syndication/"
+  xmlns:slash="http://purl.org/rss/1.0/modules/slash/"
+  >
   <channel>
-    <title>{{ site.name }}</title>
+    <title xml:lang="en">{{ site.name }}</title>
+    <atom:link type="application/atom+xml" href="{{ site.url }}/rss.xml" rel="self"/>
+    <link>{{ site.url }}/</link>
+    <pubDate>{{ site.time | date: "%a, %d %b %Y %H:%M:%S %z" }}</pubDate>
+    <lastBuildDate>{{ site.time | date: "%a, %d %b %Y %H:%M:%S %z" }}</lastBuildDate>
+    <language>en-US</language>
     <description>{{ site.description }}</description>
-    <link>{{ site.url }}</link>
-    <atom:link href="{{ site.url }}/feed.xml" rel="self" type="application/rss+xml" />
     {% for post in site.posts limit:10 %}
       <item>
         <title>{{ post.title }}</title>
@@ -18,6 +28,12 @@ layout: none
         {% else %}
         <link>{{ site.url }}{{ post.url }}</link>
         {% endif %}
+        {% for tag in post.tags %}
+        <category>{{ tag | xml_escape }}</category>
+        {% endfor %}
+        {% for cat in post.categories %}
+        <category>{{ cat | xml_escape }}</category>
+        {% endfor %}
         <guid isPermaLink="true">{{ site.url }}{{ post.url }}</guid>
       </item>
     {% endfor %}