Finalize TimeControl PGN header support

[niklasf]

After #1032:

• Implement setter

[eminyous]

I am trying to understand the task on this issue and may be implementing it. But I don't understand where do you want to add a setter? Is it in the Game class or other?

[niklasf]

Yes, next to

python-chess/chess/pgn.py

Line 896 in e773cd4

def time_control(self) -> TimeControl: