Some users may use filtering but not have the "clean transparent"
filter enabled in the Minetest engine config. Bake this filter
into all images to (1) avoid the consequences of this (i.e. black
halos), and (2) possibly speed up startup time (the filter will
converge immediately).
- Consolidate any "source-only" files into "src" dirs.
- Exclude "docs" dir, mainly in root atm.
- Exclude all dotfiles.
This significantly reduces the size of delivered files, since
esp the player model .blend file is very large.
