add step limit
indent fix
fix type error
bug fix
bug fix, import socket in main.py
Bug Fix

1. in `main.cpp` and `chess.py`: fix bug for invalid message
2. in `network.cpp`: close socket when server is exiting
in main.py, bug fix for send failure
bug fix
Merge pull request #4 from abcdabcd987/master

bug fix and add step limit