Show timestamp in Blog post pages

When reading the blog, it is confusing not to see the date when a post was written. 

For instance [this post](http://emberjs.com/blog/2013/05/03/ember-data-progress-update.html) starts with this text "Just over a month ago, we told you about".
Having the timestamp at the top of the post can be helpful to understand exactly what the post is talking about.