code: function(all) {
        var str = this;
        if(all !== false) {
          str = str.zenkaku('k');
        }
        return str.replace(/[\u30A1-\u30F6]/g, function(c) {
          return c.shift(-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'
  
  *