private HttpRequest.Builder newHttpRequest(String url) {
    return HttpRequest.newBuilder(URI.create(url))
      .timeout(config.httpTimeout())
      .header(USER_AGENT, config.httpUserAgent());
  }
Starts downloading all resources in parallel, logging progress until complete.

@throws IllegalStateException if an error occurs downloading any resource, will be thrown after all resources
                              finish
planetiler-core/src/main/java/com/onthegomap/planetiler/util/Downloader.java