Add player and inventory saving

[OneAvargeCoder193]

This makes the player's position and inventory save at a 5 second interval.

[IntegratedQuantum]

It seems to work! I can't wait to merge this, this will be so helpful in further testing.
But there are a few small things that I'd like you to fix first.

[IntegratedQuantum]

There were still some small problems left, like you forgot to change replace buffer in one place, but I decided to just fix them myself so we can merge this faster.