Volcanic Update

Here's a sneak WIP preview of the next update, a volcanic biome featuring lava flows, reworked volcano tiles and black sand beaches.

I'm also going to be revising the mountain tiles in general. If you've noticed that the big mountain tiles in the tileset are never in any of my mock-ups... well, it's because I've never been happy with them and I want to get them polished up and tiling correctly. I'm also trying to figure out some mountain tiles with lava flows so you can have the lava starting in the mountains.