implement 'resume' feature for a running game

this commit implement a feature to pause a running game session and resume it again.
the game will start from where you left it.

on pressing `spacebar`, a running game session will get paused and game's score and position data will be saved.
command `term2048 --resume` will resume the game and start it from where you paused the game.
* We must break the function here with a `return` to avoid executing the rest of the code.
* In `ui.py` we might want to display a warning if it didn’t work
* We need to know if the program was able to parse the file for unit testing