Add a _global_ collection

_global/404.html

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+---
+layout: default
+---
+
+<style type="text/css" media="screen">
+  .container {
+    margin: 10px auto;
+    max-width: 600px;
+    text-align: center;
+  }
+  h1 {
+    margin: 30px 0;
+    font-size: 4em;
+    line-height: 1;
+    letter-spacing: -1px;
+  }
+</style>
+
+<div class="container">
+  <h1>404</h1>
+
+  <p><strong>Page not found :(</strong></p>
+  <p>The requested page could not be found.</p>
+</div>

_global/feed.xml

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+---
+layout: null
+---
+<?xml version="1.0" encoding="utf-8"?>
+<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">
+  <channel>
+    <title>{{ site.title }}</title>
+    <description>{{ site.description }}</description>
+    <link>{{ site.url }}</link>
+    {% include /functions/wiki-pages.html %}
+    {% for post in wiki_pages reversed%}
+      {% unless post.draft %}
+        <item>
+          <title>{{ post.title | xml_escape }}</title>
+          <description>{{ post.description | xml_escape | truncate: 300 }}</description>
+          <pubDate>{{ post.created | date_to_xmlschema }}</pubDate>
+          <link>{{ post.url | prepend: site.url | append: '.html'}}</link>
+          <guid isPermaLink="true">{{ post.url | prepend: site.url  | append: '.html' }}</guid>
+        </item>
+      {% endunless %}
+    {% endfor %}
+  </channel>
+</rss>

_global/index.html

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+---
+layout: redirect
+---

_global/tags.html

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+---
+layout: default
+title: Tags
+---
+{% assign var = 10 %}
+
+{% comment %}
+=======================
+The following part extracts all the tags from your posts and sort tags, so that you do not need to manually collect your tags to a place.
+=======================
+{% endcomment %}
+{% assign rawtags = "" %}
+
+{% include /functions/wiki-pages.html %}
+
+{% for wiki_page in wiki_pages %}
+	{% assign ttags = wiki_page.tags | join:'|' | append:'|' %}
+	{% assign rawtags = rawtags | append:ttags %}
+{% endfor %}
+{% assign rawtags = rawtags | split:'|' | sort %}
+
+{% comment %}
+=======================
+The following part removes dulpicated tags and invalid tags like blank tag.
+=======================
+{% endcomment %}
+
+{% assign tags = "" %}
+{% for tag in rawtags %}
+	{% if tag != "" %}
+		{% if tags == "" %}
+			{% assign tags = tag | split:'|' %}
+		{% endif %}
+		{% unless tags contains tag %}
+			{% assign tags = tags | join:'|' | append:'|' | append:tag | split:'|' %}
+		{% endunless %}
+	{% endif %}
+{% endfor %}
+
+<ul>
+{% for tag in tags %}
+	<li id="n-tag-{{ tag }}"><a href="/{{ site.data.i18n[site.lang].prefix.tag }}{{ tag }}.html">{{ tag }}</a></li>
+	<ul>
+	{% for other_page in wiki_pages %}
+	{% if other_page.tags contains tag %}
+	<li><a href="{{ other_page.url }}">{{ other_page.title }}</a></li>
+	{% endif %}
+	{% endfor %}
+	</ul>
+{% endfor %}
+</ul>