Top level header should be HTML level 1

Perhaps the former way was done because someone considered
the use of <h2> to produce a result that "looks nicer". But
if so, the proper solution would be to adjust the styling
for level 1 headers, not to use a level 2 header.

Author: fingolfin

_layouts/default_with_title.html

@@ -1,5 +1,5 @@
 ---
 layout: default
 ---
-<h2>{{ page.fulltitle | default: page.title }}</h2>
+<h1>{{ page.fulltitle | default: page.title }}</h1>
 {{ content }}