New documentation

First commit, halfway through a major restructuring of documentation.

docs/_includes/commento.html

@@ -0,0 +1,5 @@
+{% unless page.comments == false %}
+<div id="commento"></div>
+<script src="https://cdn.commento.io/js/commento.js"></script>
+<noscript>Please enable JavaScript to load the comments.</noscript>
+{% endunless %}