Engine: Improved character walking at 60%-80% scaling

Courtesy of Alan v. Drake.
Scrapped the extended savedgame format

This reverts 453ff96 and a small piece of 709b63c commit.

I overlooked the fact that the all reserved option slots are serialized as a part of GameSetupStructBase serialization, therefore there's no need to write new ones separately.
Compatibility: handling null string pointer in formatted print for < 3.2 games