Elasticsearch 7 and association preloading

[liamwhite]

1. Adds (breaking) support for Elasticsearch 7, which has changed the way that total hits are returned
2. Allows associations to be preloaded by the paginate method, like so:

  def index(conn, params) do
    query = %{query: %{match_all: %{}}, sort: %{created_at: :desc}}
    opts = %{options: [queryable: from(i in Image, preload: :user)]}

    images = ESx.search(Image, query) |> ESx.paginate(Map.merge(params, opts))

    render conn, "index.html", images: images.entries
  end

[ikeikeikeike]

Hello, @liamwhite! This is your first Pull Request that will be reviewed by Ebert, an automatic Code Review service. It will leave comments on this diff with potential issues and style violations found in the code as you push new commits. You can also see all the issues found on this Pull Request on its review page. Please check our documentation for more information.

[ikeikeikeike]

Ebert has finished reviewing this Pull Request and has found:

• 1 possible new issue (including those that may have been commented here).

You can see more details about this review at https://ebertapp.io/github/ikeikeikeike/scrivener_esx/pulls/1.