TODO

- optimizations
-- use heightmap equivalent for voxelization/downsample
-- use 1 bit per voxel for last level (16x memory save)
- better pathfind
-- use same string-pulling idea for navvolumes
-- follow/target update
- intersectionset dirty roots?
- per-zone custom markup
-- tighter borders / set of regions to ignore geometry outside
- volume nav - consider building equivalent of navmesh
-- do we even need any compact representation? connectivity sounds hard for 3d spans...
-- watershed-like partitioning - should be easy
-- contour tracing - moderate?
-- contour simplification - easy
-- building simple polys - moderate?
-- earcut triangulation - easy?
-- theta* on mesh - easy?
- jump / drop markup (offmesh connections?)
- area transitions & high-level zone graph