This reverts commit 467fc0dd.

Add schematic decoration force placement flag

Add find_surface_nodes_in_area LUA call which permit to only get the nodes which touch air. This permit to massively improve performance for mods like plantlife

Rebased by Zeno- (conflict in lua_api.txt)

Client now informs about incompatible servers from the list, this permits to prevent the protocol movements.
Server announces its supported protocol versions to master server

Also add a Lua API and chatcommand for this

Lua-api.txt: Document that paramtype='light' results in light propagation with attenuation and is essential for a light source to spread it's light

Just Markdown, no variant of it. File name intentionally
not changed to “lua_api.md” because of fear to break references
to that file. The file can still be renamed later.

Also rewrite mapgen registration for static initialization

Add minetest.get_mapgen_params()
Deprecate minetest.register_on_mapgen_init()

Also set default height_min/height_max to -31000 and 31000,
respectively, for ore and biomes

If CMake is run and Doxygen is found, add a make target called "doc",
which builds API documention in doc/html. This target is not included
in the default "all" target, you have to explicitly run "make doc" to
generate the documentation.

If graphviz is installed, in particular, if the "dot" binary is found,
doxygen is configured to generate various kinds of diagrams. Note that
due to this, the first run of doxygen can take a while.