Add Schema.org markup to blog posts

The main search engines (Google, Bing, Yahoo) use mircodata for rich snippets in their search results. They use the [Schema.org](http://schema.org/) markup.

This PR adds the necessary microdata to blog postings. I validated the output using Google's [Structured Data Testing Tool](https://www.google.com/webmasters/tools/richsnippets)

I also removed the pubDate attribute from time tags. Its been removed from the HTML5 spec and was the only thing stopping full HTML5 validation.