1.3.1 - Savegame bugfixes

This update is only a bugfix update while I am working on the Puzzle DLC :)

Unfortunately, in the past there was the occasional case that a save was corrupted, for example if the computer crashed while saving.

The 1.3.1 update now makes a backup before each save, and saves the file first to a temporary file, and then moves it. This means that a lot would have to go wrong for a save to be lost, and even then the game still keeps a backup of the save.

I hope that now no saves are lost and I apologize for all lost saves so far!