code: static Startup fromFileList(List<String> fns, String context, MessageHandler mh) {
          List<StartupEntry> entries = fns.stream()
                  .map(fn -> readFile(fn, context, mh))
                  .collect(toList());
          if (entries.stream().anyMatch(sue -> sue == null)) {
              return null;
          }
          return new Startup(entries);
      }
docs: Factory method: Read Startup from a list of external files or resources.
  
  @param fns list of file/resource names to access
  @param context printable non-natural language context for errors
  @param mh handler for error messages
  @return files as Startup, or null when error (message has been printed)