Dumbest possible Jekyll plugin: prefix site.baseurl

site_url.rb

# {% site_url /some/path/to/file.suffix %} is like {{ '/some/path/to/file.suffix' |:prefix site.baseurl }}
module Jekyll
  class SiteUrl < Liquid::Tag

    def initialize(name, url, tokens)
      super
      @url = url
    end

    def render(context)
      context.registers[:site].baseurl+@url
    end
  end
end