TallGrass

Added a tall grass finisher.

Makes double tall grass
different densities for different biomes.
Do you require the grass patches to be this "smooth", or could they be totally random?

I think random would be okay and you could save on performance here by using `IntNoise2DInt` instead; divide the value by a small prime (7), then modulo by 100 and compare to the threshold; let the `BiomeDensity` be an int between 0 and 100. No need to adjust the coords, use raw block coords in the chunk as the noise's coords.