CustomBlocks - shrunk block selections

[Cervator]

Getting this into an issue for down the road. Idea is to take a square area, place blocks of your choice in it, and shrink it down to dynamically fashion a new block. Example: Stairs

Somewhat similar to #256, but this is simpler (if still tricky and full of consequences) if started from binary numbers and the output being exactly one standard sized block (2x2x2 -> 1 block or 4x4x4 -> 1 block, etc)

Might be potential for arbitrary sizing and so forth as well, but baby steps and all that