Resolves #692 - Quicksaving

Split game::autosave() into two - quicksave() handles the vehicle, movement and item checks (i.e. anything that could potentially lead to problems by saving rapidly or due to bugs) and then handles the saving. autosave() handles the time-delay checks and then calls quicksave()

Removed some copypasta'd autosave() code and replaced it with quicksave().

keymap not updated, I'd recommend 'q' as the quicksave key.

Note: It appears that NPCs teleport a few tiles south upon saving/loading. I'm fairly certain that's not to do with these changes however.