Add support for documentation fields

Grape exposures give you entity_name, exposures and documentation. We can add those for out-of-the-box support for https://github.com/tim-vandecasteele/grape-swagger.

module Grape
  module Roar
    module Representer
      def self.included(base)
        base.extend(ClassMethods)
      end

      module ClassMethods
        def entity_name
          self.name.split('::').last.gsub(/Presenter$/, '')
        end

        def exposures
          {}
        end

        def documentation
          Hash[representable_attrs.map do |attribute|
            property_name = attribute[:as].evaluate nil, nil
            next if property_name == '_links'
            [ property_name, { desc: attribute[:desc], type: attribute[:type] }]
          end.compact]
        end
      end
    end
  end
end

Start at Grape::Roar::Representer::ClassMethods and compare the existing representer behavior with the proposed entity_name, exposures, and documentation entry points. Check how grape-swagger consumes these fields, then add coverage for the three fields, including the documented _links exclusion. Done means out-of-the-box grape-swagger support works for Grape exposures.