docs: function normalize(keywords, options) {
    var opts = _.extend({inflect: false}, options);
  
    keywords = _.union(keywords, chop(keywords));
    var omit = exclude(opts.omit);
  
    var res = keywords.map(function (keyword, i) {
      if (options && options.normalize) {
        return options.normalize(keywords, i, keywords);
      }
      return properize(keyword, options);
    }).sort();
  
    return _.uniq(_.difference(res, omit));
  }