more interesting terrain

[bfops]

change terrain gen from a 2d heightmap to a 3d heightmap, and then create a mesh using something like isosurface extraction (create polygons only for chunks that cross a +/- boundary in the perlin noise)

[bfops]

Consider ditching perlin noise, or only using it as a coarse basis for more interesting terrain gen. Eventually we'll probably want multiple passes, for placing things like trees, houses, etc.

[bfops]

We'll almost definitely want voxels or tiles for terrain generation. That might also also fit in with incremental loading/unloading (#84).

[bfops]

Trees or houses would be nice.

[bfops]

trees eaf089a

[bfops]

Continued in #117.