Describe the feature

I want a Slab + Edge Slab block put together to form a stair block.

I made this example with Chisel & Bits, but their blocks get laggy quickly because of the amount of data they need to store in each block, so I want a block that will work from your mod.

This kind of block is already planned, I'm still looking for a good name though. Keep an eye on #165 to follow the progress.