Added support for artibtrary tags and autotagging

Hi, I added two things to your library.

1) It goes through and adds all of the metatags that were set:
        meta_tags.each do |name,content|
          result << tag(:meta, name: name, content: content ) unless content.blank?
        end

2) There's an autotagger, which looks at the current_page.data and site data to help setup twitter cards and open graph stuff.