code: function loadNunjucks(filtersModule) {
    if (fs.existsSync(filtersModule)) {
      try {
        const filters = require(filtersModule);
        nj = templater.loadNjEnv(filters.sync, filters.async);
      } catch (e) {
        console.log('Failed to load Nunjucks environment: ', e);
        process.exit(1);
      }
    }
    else {
      try {
        nj = templater.loadNjEnv();
      } catch (e) {
        console.log('Failed to load Nunjucks environment: ', e);
        process.exit(1);
      }
    }
  }
docs: instantiate nunjucks, include filters if they exist: