Godot: main menu and simple saving system

A base for your game, which include main menu with simple setting, archive and credit.

Feel free to use it, just give me a credit, I guess.

Note that you can't change scene by using "get_tree().change_scene_to_file("res://your_scene.tscn")" due to the structure of this project, instead, you have to implement it like I do in the "main_menu.gd", I may make another one that is able to change scene normally in the future though.