code: function processTokens(tokens, callback) {
      "use strict";
      var processFunctions = underscore.map(tokens, function (word) {
          return function (cb) {
              tokenizeWord(word, cb);
          };
      });
      async.parallel(
          processFunctions,
          function (error, results) {
              if (error) {
                  callback(error, null);
              } else {
                  var normalizedTokens = [];
                  results.forEach(function (tokens) {
                      normalizedTokens = normalizedTokens.concat(tokens);
                  });
                  normalizedTokens.sort();
                  normalizedTokens = underscore.uniq(normalizedTokens, true);
                  callback(null, normalizedTokens);
              }
          }
      );
  }
docs: Processes each word of the given tokens
  
  @param String[] tokens Array of Strings
  @param Function callback Callback function with this signature: function(error, String[])
  @private