- Use `unique_ptr` instead of manually memory management
- All of its methods now perform bounds checking in release builds. The
exception is `*Unchecked` methods.
- Use an anonymous namespace for local definitions in `VoxelModel.cpp`
- `VoxelModel::LoadKV6` methods now returns `Handle<_>` and accepts
`IStream &`.
- Delete the copy constructor and assignment operator
- Remove debug code
