On the lua side, notably minetest.env:<function>(<args>) should now
be replaced by minetest.<function>(<args>).
The old way is and will stay supported for a long time.

Also:
Update and clean up lua_api.txt (by celeron55)
Move EnvRef to lua and remove add_rat and add_firefly (by kahrl)
Add separate src/util/CMakeLists.txt, other minor fixes (by kahrl)

Add after_destruct and cache the existence of on_construct, on_destruct and after_destruct for quick skipping when a node does not have them

Make the minimal development test somewhat playable by adding ore generation and removing the player visual switch test