text: Title: example rand_exit_choice_nb can not run
  Body: Hi, 
  
  I find an example can not run:
  
  https://github.com/polakowo/vectorbt/blob/master/vectorbt/signals/factory.py#L316
  
  ```python
    File "D:\Users\Kan\miniconda3\envs\py38_vectorbt\lib\site-packages\vectorbt\signals\factory.py", line 61, in __init__
      IndicatorFactory.__init__(
  TypeError: __init__() got an unexpected keyword argument 'in_output_settings'
  ```
  
  
  ```python
    File "D:\Users\Kan\miniconda3\envs\py38_vectorbt\lib\site-packages\vectorbt\signals\factory.py", line 61, in __init__
      IndicatorFactory.__init__(
  TypeError: __init__() got an unexpected keyword argument 'param_settings'
  ```
  
  ```python
  Traceback (most recent call last):
    File "D:/test_vectorbt/demo_stop3.py", line 66, in <module>
      my_sig.rand_type_readable
    File "D:\Users\Kan\miniconda3\envs\py38_vectorbt\lib\site-packages\vectorbt\indicators\factory.py", line 1181, in attr_readable
      return getattr(_self, attr_name).applymap(lambda x: '' if x == -1 else enum._fields[x])
    File "D:\Users\Kan\miniconda3\envs\py38_vectorbt\lib\site-packages\pandas\core\frame.py", line 6944, in applymap
      return self.apply(infer)
    File "D:\Users\Kan\miniconda3\envs\py38_vectorbt\lib\site-packages\pandas\core\frame.py", line 6878, in apply
      return op.get_result()
    File "D:\Users\Kan\miniconda3\envs\py38_vectorbt\lib\site-packages\pandas\core\apply.py", line 186, in get_result
      return self.apply_standard()
    File "D:\Users\Kan\miniconda3\envs\py38_vectorbt\lib\site-packages\pandas\core\apply.py", line 313, in apply_standard
      results, res_index = self.apply_series_generator()
    File "D:\Users\Kan\miniconda3\envs\py38_vectorbt\lib\site-packages\pandas\core\apply.py", line 341, in apply_series_generator
      results[i] = self.f(v)
    File "D:\Users\Kan\miniconda3\envs\py38_vectorbt\lib\site-packages\pandas\core\frame.py", line 6942, in infer
      return lib.map_infer(x.astype(object).values, func)
    File "pandas\_libs\lib.pyx", line 2329, in pandas._libs.lib.map_infer
    File "D:\Users\Kan\miniconda3\envs\py38_vectorbt\lib\site-packages\vectorbt\indicators\factory.py", line 1181, in <lambda>
      return getattr(_self, attr_name).applymap(lambda x: '' if x == -1 else enum._fields[x])
  TypeError: tuple indices must be integers or slices, not float
  ```
  
  
  
  