Add new events. Implement bind/unbind/emit in EventManager
Merge branch 'master' of github.com:ZhanruiLiang/sys-analysis
ADD: debug module.
MODIFY: Display class. Add method `init`
MODIFY: events.py

* move all event type constants into class EventTypes.
* add docstring for Event class.
MODIFY: game.py. Added method `join_player`. Changed `configData` format in method `setup_stage`.  Updated the main loop.
rename inputManager.py to input.py.
Add game logic in world.py. Trival bugs still exist.
Add new members in class `Snake`.
Move `Directions` from snake.py to grids.py. Add `__repr__` for class `Field`.
Add method and members into base class `Player`.
update .gitignore.