make_pairs is better.
externalize/unhardcode sprites.

hard coding is gone. the ability to add/replace the bullet sprites is now
available.

also adds the ability to subdivide ruleset defined spritesheets.

adds a lot more readability to the extraSprites and extraSounds functions.
fix some score calculations regarding unconscious/dead aliens
make file dot ayem
make file?
paranoia that modders won't use correct sized images for projectiles.
fix some AI stuff

blaster bombs shouldn't pathfind through closed doors.
aliens shouldn't be constantly hiding
isBlocked, not isPassable.
slightly better efficacy
fix charging issue.
fix seeing in the dark
fix bullet sprite positioning
whoops.
shade level, not light level.
fix some melee targetting stuff.

change VectorToDirection to be a static member of Pathfinding.cpp, just
like it's cousin, DirectionToVector.

change the ValidMeleeRange check to actually trace a trajectory rather
than checking the pathfinding validity.

adjust said method to actually account for stairs and ramps properly,
and get rid of the "-1" case
fix "cautious" behaviour

damage > 50%? disengage!
fix disappearing cursor on battle end.

and make cautious use >=  instead of >
fix auto battle end

queue up the end battle action instead of pushing it directly.
fix fire/smoke propegation and damage

fire should only spread in the four cardinal directions.
smoke should only come as a result of fire when the fire goes out.
smoke should not spread into burning tiles.
units should be hit by fire if it spreads into the tile they occupy.
likewise for smoke.
fix some visibility stuff

whenever lighting gets updated, or terrain is potentially destroyed,
recalculate FOV