Add application/ld+json to posts and pages

[marcofranssen]

This PR adds a new feature to the theme to include https://jsonld.com/blog-post/ to every blogpost and page.

[ppoffice]

@marcofranssen I saw you hard-coded author name in the script. Could you please replace it with <%= author %>? Also, I'm not sure if every post has post.update and post.title. Maybe we should wrap those two lines with if.

[marcofranssen]

Updated the PR, one question though! How do I get rid of the whitelines when the if is evaluated false?

[ppoffice]

@marcofranssen You probably can construct the JSON data as a whole and print it out. Or use some minifier.