def fget(url, version: nil, locale: nil)
      @client.fget(url, headers: headers(version: version, locale: locale))
    end
def fget(url, version: nil, locale: nil)
      @client.fget(url, headers: headers(version: version, locale: locale))
    end
Like {#get}, but schedules any request in the background using a thread
 pool. Handy to issue lots of requests in parallel.

 @return [ResponsePromise], which responds to `status`, `headers`, and `body`
 like [Response].