Proper world generation

Add a proper world generation API and implement:

• Flat
• Normal
• Random (like, random blocks)
  ...

[haykam821]

I’ll work on implementing this. I don’t see a way to make them compatible with the other world generators since those are chunk-based. Should there be a configurable function called with the X, Y, and Z coordinates that returns the block ID to put in that position?

That's an option, traditionally generators are given a X and Z for the chunk, then it returns the entire 16x16x256 (or whatever the world and chunk size is set to) array of blocks.