Grape Entity Support

[calebwoods]

Inspired by the on pull request #30 by @TLmaK0, this pull request adds support for generating swagger responseClass and models per the Swagger API Declaration based on Grape Entities.

Usage would look like the following

module API

  module Entities
    class Status < Grape::Entity
      expose :text, :documentation => { :type => "string", :desc => "Status update text." }
    end
  end

  class Statuses < Grape::API
    version 'v1'

    desc 'Statuses index', {
      :entity => API::Entities::Status
    }
    get '/statuses' do
      statuses = Status.all
      type = current_user.admin? ? :full : :default
      present statuses, with: API::Entities::Status, :type => type
    end
  end
end

And would generate the following swagger json

{
  "apiVersion": "0.2",
  "swaggerVersion": "1.1",
  "basePath": [..],
  "resourcePath": "/statuses.{format}"

  ...

  "apis" : [...]
  "models": {
    "Status": {
      "id": "Status",
      "name" : "Status",
      "properties": {
         "text": {
           "type": "string",
            "desc": "Status update text."
         }
      }
    }
  }