Fix validation HTML validation errors (#62)

* Make the theme compliant with W3C standards (#55)

* Dropped the line because chrome tab is deprecated.

* On header, "li" elements are meant to surround the "a" elements and not the other way around.

* Dropped all section tags I could find at first glance, as they had no semantic meaning and were firing warnings at the W3C validator.

* Change "middot" from a helper div to a helper class since putting div's inside ul's is not compliant

* Fixed a problem of the previous commit. A middot would not hide if on mobile.

* Fix archetypes bug with Go templates

* Fix additional validation error in 404

layouts/_default/single.html

@@ -1,5 +1,5 @@
 {{ partial "header.html" . }}
-<section class="main">
+<div class="main column">
     <div class="container">
         <div class="content">
             {{ partial "page-heading.html" . }}
@@ -8,5 +8,5 @@
             </div>
         </div>
     </div>
-</section>
+</div>
 {{ partial "footer.html" . }}