def breadcrumb(key = nil, *args)
      if key.nil? || key.is_a?(Hash)
        raise ArgumentError, "The `breadcrumb` method was called with #{key.inspect} as the key. This method is used to set the breadcrumb. Maybe you meant to call the `breadcrumbs` method (with an 's' in the end) which is used to render the breadcrumbs?"
      end
      @_gretel_renderer = Gretel::Renderer.new(self, key, *args)
    end
def breadcrumb(key = nil, *args)
      if key.nil? || key.is_a?(Hash)
        raise ArgumentError, "The `breadcrumb` method was called with #{key.inspect} as the key. This method is used to set the breadcrumb. Maybe you meant to call the `breadcrumbs` method (with an 's' in the end) which is used to render the breadcrumbs?"
      end
      @_gretel_renderer = Gretel::Renderer.new(self, key, *args)
    end
Sets the current breadcrumb to be rendered elsewhere. Put it somewhere in the view, preferably in the top, before you render any breadcrumbs HTML:

   <% breadcrumb :category, @category %>

 If you pass an instance of an object that responds to +model_name+ (like an ActiveRecord model instance), the breadcrumb can be automatically inferred, so a shortcut for the above would be:

   <% breadcrumb @category %>