The even more validating release

• Changed the comment invitation box from a section to a div. (#505)
• Cleaned up a HTML validation error in the graph page. (#508)
• Cleaned up a HTML validation error in the stats page. (#509)
• Changed the links and socials headings in the sidebar to divs from h2s, leaving headings only used in the main page or article. (#512)
• Changed the heading level of post content in list views (index, archives, tags, categories) to be relative to the post title. For example, if a post uses h2 headings, they will be rendered as h3 in list views where the post title itself is an h2, maintaining a correct heading hierarchy. (#513)