Previously, walls were all numbered at 21000+. This is bad because
our blockmap is an array, so this caused our blockmap to take up
80 MiB of RAM in each worker process.
This commit changes the wall numbering, and exploits some bitmasking
to have the wall check run in constant time no matter how many walls
there are. This is done with a simple mask and xor to check the prefix.
RAM usage for the blockmap thus drops to like 44 MiB.
This is in preparation for adding more walls for 1.16.
This adds:
- mossy stone brick stairs
- mossy cobblestone stairs
- mossy stone brick walls
We also add another block class for walls, and while we're at it,
clean up the stairs texture function to not have a huge sprawling
elif mess for loading textures, but instead to a cheeky dictionary
lookup.
In case you're wondering, yes I am just as disgusted by this code as
you are.
