Ore Pockets and elevation mechanics to make Ores rarer

Ores need rebalancing, and I think that we could use the height to create layers where certain ores are more common than others, deepening the strategy in mining.

To make it work, there could be two different variations to how ores generate; exposed ores or pockets ores.

• Exposed ores are the blobs we see today that can show up on the surface of caves from time to time. These would be common, but smaller than current blobs.

• Pocket ores would essentially work like ancient debris in that they're never exposed to cave air. They could work like veins in that you get a visual clue from the stone that an ore might be hidden there.

The idea then is for exposed ores to mostly only spawn in a certain range of elevation:

• Exposed iron is more common between y=24 and y=0 and only spawns below y=24, but Pocket iron would spawn anywhere under y=48 at the same rate.

• Exposed coal is more common between y=100 and y=124. Pocket coal generates anywhere in the world.

• Exposed diamond is more common deep in the world, between y=-36 and y=-64, but Pocket diamond could be rare and generate all the way up to y=-12, as a nice surprise for people mining.

Lapis and Coal being rarer underground could be an interesting shake-up for early game strategies, and Iron and Coal generating more commonly in two seperate regions could make the first night a lot more interesting. 

Of note, Diamonds need to be rarer in both noise caves and in structures, and Armorsmiths and Weaponsmiths need to be rebalanced.