Added self to SIGNOFF.
Improved Robust Genetics.

Without: 33% chance to pick a bad mutation, otherwise picks any mutation
With (old): 22% chance to pick a bad mutation
With (new): 33% chance to pick a good mutation
fixed permissions from executable to read/write on disease.h
* removed a stupid save an loading bug.
* fixed typo
* Set default value for some npc.plt.
* removed one npc.die statement from mission fail. (would cause crash).
* fixed cleanup_at_end. Added null checks to mission functions. and find mission now complains when it cannot find a mission.
* removed reset npcs code. That wasn't used nor working.
Extract most iuse firestarting logic into helper methods
Add a fire drill item (survivalcraft firestarter)
Update changelog for my major changes since 0.4
Merge pair of bugfix pull requests.
Merge mutation code refactor and adjustment of robust genetics algorithm.
Merge fire bow.
Merge pull request #2 from TheDarklingWolf/master

Update