Add posts, categories, category, tags, tag, and collection layouts

Replace sample pages with hard coded HTML and Liquid in favor of a layout that does all the heavy lifting. Assign the appropriate `layout` via YAML Front Matter and away you go.

_layouts/categories.html

@@ -0,0 +1,48 @@
+---
+layout: archive
+---
+
+{{ content }}
+
+<ul class="taxonomy-index">
+  {% assign categories_max = 0 %}
+  {% for category in site.categories %}
+    {% if category[1].size > categories_max %}
+      {% assign categories_max = category[1].size %}
+    {% endif %}
+  {% endfor %}
+  {% for i in (1..categories_max) reversed %}
+    {% for category in site.categories %}
+      {% if category[1].size == i %}
+        <li>
+          <a href="#{{ category[0] | slugify }}">
+            <strong>{{ category[0] }}</strong> <span class="taxonomy-count">{{ i }}</span>
+          </a>
+        </li>
+      {% endif %}
+    {% endfor %}
+  {% endfor %}
+</ul>
+
+{% assign categories_max = 0 %}
+{% for category in site.categories %}
+  {% if category[1].size > categories_max %}
+    {% assign categories_max = category[1].size %}
+  {% endif %}
+{% endfor %}
+
+{% for i in (1..categories_max) reversed %}
+  {% for category in site.categories %}
+    {% if category[1].size == i %}
+      <section id="{{ category[0] | slugify | downcase }}" class="taxonomy-section">
+        <h2 class="archive__subtitle">{{ category[0] }}</h2>
+        <div class="entries-{{ page.entries_layout | default: 'list' }}">
+          {% for post in category.last %}
+            {% include archive-single.html %}
+          {% endfor %}
+        </div>
+        <a href="#page-title" class="back-to-top">{{ site.data.text[site.locale].back_to_top | default: 'Back to Top' }} &uarr;</a>
+      </section>
+    {% endif %}
+  {% endfor %}
+{% endfor %}