Uniformize headers in simple theme

In the simple theme, some templates are using `h1`, others are using
`h2` for the main title of the page (other than the one in the header).
This commit changes that so all of the pages are using `h1`.

pelican/themes/simple/templates/article.html

@@ -24,9 +24,9 @@
 {% block content %}
 <section id="content" class="body">
   <header>
-    <h2 class="entry-title">
+    <h1 class="entry-title">
       <a href="{{ SITEURL }}/{{ article.url }}" rel="bookmark"
-         title="Permalink to {{ article.title|striptags }}">{{ article.title }}</a></h2>
+         title="Permalink to {{ article.title|striptags }}">{{ article.title }}</a></h1>
  {% import 'translations.html' as translations with context %}
  {{ translations.translations_for(article) }}
   </header>

pelican/themes/simple/templates/author.html

@@ -3,6 +3,6 @@
 {% block title %}{{ SITENAME }} - Articles by {{ author }}{% endblock %}
 
 {% block content_title %}
-<h2>Articles by {{ author }}</h2>
+<h1>Articles by {{ author }}</h1>
 {% endblock %}
 

pelican/themes/simple/templates/category.html

@@ -3,6 +3,6 @@
 {% block title %}{{ SITENAME }} - {{ category }} category{% endblock %}
 
 {% block content_title %}
-<h2>Articles in the {{ category }} category</h2>
+<h1>Articles in the {{ category }} category</h1>
 {% endblock %}
 

pelican/themes/simple/templates/tag.html

@@ -3,5 +3,5 @@
 {% block title %}{{ SITENAME }} - {{ tag }} tag{% endblock %}
 
 {% block content_title %}
-<h2>Articles tagged with {{ tag }}</h2>
+<h1>Articles tagged with {{ tag }}</h1>
 {% endblock %}