What's Changed
* Prevented potential errors with the SF process, and misc. by johndoknjas in https://github.com/zhelyabuzhsky/stockfish/pull/80
* If the user calls the `__del__` method themselves, this could potentially result in an error, since the OS may call `__del__` later. So in each call to `__del__`, ensure that self._stockfish is still running (i.e., `= None`).
* A check is also implemented in the _put function, such that if self._stockfish isn't running, or if the "quit" command has already been sent to Stockfish, then the stdin.write() and stdin.flush() lines won't be executed.
* **Renamed the self.stockfish instance variable to self._stockfish**, in order to indicate that it should be treated as private.
* Changed the default search depth from 2 to 15, in case the user doesn't set it themselves. 15 is a good depth value since it's nearly instantaneous while still being fairly strong.
* Added to the example in the readme for creating a Stockfish instance, in order to show how to send all the optional arguments together.
* Fixed README.md by zhelyabuzhsky in https://github.com/zhelyabuzhsky/stockfish/pull/82
**Full Changelog**: https://github.com/zhelyabuzhsky/stockfish/compare/3.21.0...3.22.0