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.

_includes/documents-collection.html

@@ -0,0 +1,19 @@
+{% assign entries = site[include.collection] %}
+
+{% if include.sort_by == 'title' %}
+  {% if include.sort_order == 'reverse' %}
+    {% assign entries = entries | sort: 'title' | reverse %}
+  {% else %}
+    {% assign entries = entries | sort: 'title' %}
+  {% endif %}
+{% elsif include.sort_by == 'date' %}
+  {% if include.sort_order == 'reverse' %}
+    {% assign entries = entries | sort: 'date' | reverse %}
+  {% else %}
+    {% assign entries = entries | sort: 'date' %}
+  {% endif %}
+{% endif %}
+
+{%- for post in entries -%}
+  {% include archive-single.html %}
+{%- endfor -%}

_includes/posts-category.html

@@ -0,0 +1,3 @@
+{%- for post in site.categories[include.taxonomy] -%}
+  {% include archive-single.html %}
+{%- endfor -%}

_includes/posts-tag.html

@@ -0,0 +1,3 @@
+{%- for post in site.tags[include.taxonomy] -%}
+  {% include archive-single.html %}
+{%- endfor -%}