Adds two optimized pathfinds to replace AStar over short distances

Proc 1 is called for distances of 1 tile (I recall some places use AStar to check whether adjacent turfs are reachable). Proc 2 is a very crude direct-move algorithm intended for distances of 2-3 tiles, but can be used in any context which has extremely minimal obstacles. 

I didn't take a screenshot of profiling, but I tested with ten mobs scattered around security + ten random diseases. 

Ordinary AStar: About 0.8 self CPU
Newly optimized pathfinding: About 0.04 self CPU

This is an improvement of 2000%, and the improvement was roughly mirrored for the 5-10 minutes I was testing (I'm not happy with the second proc, but at the moment it's only called for distances of 2 tiles so it's fine as-is). These two procs are primarily added as a hotfix to address the extra overhead from the new AStar added in #592, in particular from the excessive lag caused by airborne diseases (airborne diseases default to a 2 tile range, but in testing some only transferred to adjacent tiles). 

I've added this to weekly milestones, as Scaredy's currently running an out of date copy of the code (due to aforementioned diseases lag).