post-to-post pagination and a few spacing tweaks

_includes/layouts/post.njk

@@ -34,4 +34,13 @@ layout: base.njk
 
     {{ content | safe }}
   </article>
+
+  {% set olderPost = collections.posts | getPreviousCollectionItem %}
+  {% set newerPost = collections.posts | getNextCollectionItem %}
+  {% set olderHref = olderPost.url %}
+  {% set newerHref = newerPost.url %}
+  {% set olderTitle = olderPost.data.title %}
+  {% set newerTitle = newerPost.data.title %}
+  {% set inPost = true %}
+  {% include "pagination.njk" %}
 </heading-anchors>