Loads and saves blocks to region files indexed by world position, under a directory. Loads and saves blocks to the filesystem, in multiple region files indexed by world position, under a directory. Regions pack many blocks together, so it reduces file switching and improves performance. Inspired by [url=https://www.seedofandromeda.com/blogs/1-creating-a-region-file-system-for-a-voxel-game]Seed of Andromeda[/url] and Minecraft. Region files are not thread-safe. Because of this, internal mutexing may often constrain the use by one thread only. Directory under which the data is saved.