Autogenerate empty nodes

If a position attempts to move into a node that doesn't exist:

Create a new node at that position, with initial coords based on the node it's coming from.
Create symmetric adjacencies for that node based on the previous node's 2-step neighbors (in the appropriate directions)

EX in 2d (photon is P, it's moving up, bottom left E is [0,0]):

EPE
EEE
EEE

Create new node with coords [1, 3]

 N 
EPE
EEE
EEE

Check for P's left neighbor's up. If exists, connect to the new node

?  N
^
E<-P  E
E  E  E
E  E  E

Same check for p's right neighbor's up.

cdeevfrr / Photon