code: function(str, all) {
      if (all !== false) {
        str = zenkaku(str, 'k');
      }
      return str.replace(/[\u30A1-\u30F6]/g, function(c) {
        return shiftChar(c, -96);
      });
    }
docs: *
  @method hiragana([all] = true)
  @returns String
  @short Converts katakana into hiragana.
  @extra If [all] is false, only full-width katakana will be converted.
  
  @example
  
  'カタカナ'.hiragana()   -> 'かたかな'
  'コンニチハ'.hiragana() -> 'こんにちは'
  'ｶﾀｶﾅ'.hiragana()       -> 'かたかな'
  'ｶﾀｶﾅ'.hiragana(false)  -> 'ｶﾀｶﾅ'
  
  @param {boolean} all
  
  *