code: async function json(url, callback, pubSub) {
    // Fritz: What is going on here? Can someone explain?
    if (url.indexOf('hg19') >= 0) {
      await sleep(1);
    }
    // console.log('url:', url);
    return fetchEither(url, callback, 'json', pubSub);
  }
docs: Send a JSON request and mark it so that we can tell how many are in flight
  
  @param url: URL to fetch
  @param callback: Callback to execute with content from fetch