Include iterator over all valid moves

[SirRender00]

Should be able to do things like

• (ActionType.RAISE, 50) in game.get_all_available_moves()
• ActionType.CALL in game.get_all_available_moves()
• (ActionType.CHECK, None) in game.get_all_available_moves()
• (ActionType.CHECK, 50) in game.get_all_available_moves() # True
• for action, val in game.get_all_available_moves(): print(action, val)

All in operations should be completed in O(1) time in the number of possible moves and chips.

[SirRender00]

@gustavomfb Hey! Glad to have you interested in contributing to the package.

What were your thoughts on implementing this one?