possible multipoint optimization

Extra lists might be slow... should try sometime.

one stack for neighbors to explore.

when under analysis add (x,y) to tracker set.

Writer func to return all higher, lower, and equal neighbors.

create 3 lists - H, L, E (or 1 hash?)
run HLE func, 
if not (existence check against tracker)
Add to H, L, E depending on relative height.
if an E, also add to main stack of EH neighbors.
