Saving, loading and main menu added

With this update the prototype now checks all the minimal viable product boxes.
It saves, it loads. There's a main menu.
There is very basic gameplay.

So the next thing to do is to expand the gameplay and  improve the movement and mouse motion.
I intend to lean into a theme of spells for digging and building. 
The 'swing a pickaxe' digging market is well covered. Lets dig by throwing fireballs. 

I dont know yet where it will go, I have several ideas but there is a gap between having the idea and actually coding it. 
Some of it might might not be feasible or outside of my current skillset.

The code is set up to be easily expandable.
The code that saves the player position and rotation for example, actually saves the position and rotation of all moving objects. 
Currently that's only the player, but if another moving object is added, no changes should be needed in the save code.
I should also be able to add a new tile type without needing to change other code.

That's all nice in theory, but in reality some bug will become apparent and some fixing will be necessary but the basic code layout should be good.

Apologies for the delay between updates, but I was sick for a week and a half.

Changenotes:

The game now autosaves on a clean exit.
If you're worried about crashing or prefer closing games with alt F4 (why though, why, but I do know people who prefer doing that) you can also press F9 to save.
Saving and loading the terrain was easy, it doesnt move and it's already stored in dictionaries.
Loading the player was more challenging.

A main menu was also added, but it's still very sparse. It has two buttons, a quit button and a 'start a new game' or 'continue' button depending on wether a savefile is present in the save folder or not.

Screenshots (F12) are now stored in the screenshot folder.