code: function split(str, separator) {
      separator = separator || '';
      if (_.isString(str)) {
          return str.split(separator);
      } else {
          return str;
      }
  }
docs: The split filter takes on a substring as a parameter.
  The substring is used as a delimiter to divide a string into an array.
  
  {{ 'a-b-c-d' | split '-' }} => [a,b,c,d]