Make sites easier to cite

[Ainali]

I read the blog post HTML Markup for Citation Tools and it seems like there are a few small things we can improve on head.liquid to make the sites that use the theme easier to cite:

• <meta property="og:title" content="{{ page.title }}">
• <meta property="og:site_name" content="{{ site.title }}">
• <meta property="og:article:published_time" content="{{ site.time | date_to_xmlschema }}">