Allow to change the dir of save

Created by: Renkineko

A comment on irc from jukado :

The game is portable (no install required), so you could put the engine with a quest on a usb stick and play to the game on multiple pc just by plugin the stick. When you do this, you don't want to lose your savefile. Savefile should be allowed in the same folder as the quest or the engine.

Another purpose (the real one from jukado) : if you want to make the demo of your quest in your usb stick, you don't want the demo to install/use any file on the computer, just on the stick.

No idea how to do that. For the second point, as the quest maker, you could setup the quest.dat with this information, but for the first optic, not sure how to do this.