text: Title: Change `Screener.set_predefined_body` and `Screener.set_body` to respond with the class
  Body: I want to change `Screener.set_predefined_body` and `Screener.set_body` to respond with the class.
  
  This would reduce
  
  ```python
  s = yf.Screener()
  s.set_predefined_body("day_gainers")
  r=s.response
  ```
  to
  ```python
  r = yf.Screener().set_predefined_body("day_gainers").response
  ```
  or to be able to set it on initialisation
  ```python
  r = yf.Screener(body="day_gainers").response
  ```
  
  
  which I think is cleaner and more concise. I would also suggest editing the docs of `predefined_bodies` as they come above `set_predefined_body` to include how to set the Screener to them 