Added support for artibtrary tags and autotagging

[wschenk]

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.

[tiste]

Thanks for contributing, I'll have a look asap :+1: