Cave biomes determined by surface biome

[careeoki]

Sandstone caves in deserts, Glacite caves in snowy biomes, etc.

[IntegratedQuantum]

It would probably end up being a rather rough approximation, since the resolution of the cave biomes is much lower than the resolution of surface biomes. But it would be a good improvement nonetheless.

I guess one important question would be how deep these should reach.

[careeoki]

Hard to say exactly since we don't have any gameplay to test it with, but they should be pretty substantial, like in Terraria. Maybe down to -256? Something in #231 territory for sure.