Replacing empty chunks that allocate lots of
memory with EmptyChunks that don’t.
Lowering the byte count for MapBlock and Chunk by 
removing obvious redundancies
Merges remote branch 'upstream/feature_ignore_airblocks' into branch minecraft.
Introduce a way to update individual blocks from
empty to non-empty in EmptyChunks
Merge remote-tracking branch 'upstream/feature_ignore_airblocks' into minecraft
a script for scraping block textures.
replace aspect_ratio by second visual angle.
replace Jonas' texture by the more complete block images from gamepedia.