code: function flip(obj) {
                var newObj = Object.create(null),
                    key;
  
                for (key in obj) {
                  newObj[obj[key]] = key;
                }
  
                return newObj;
              }
docs: Exchanges all keys with their associated values in an object.
  
  @param {Object.<string, string>} obj An object of strings.
  @return {Object.<string, string>} An object of strings.