* Add minetest.bulk_set_node call + experimental mod unittest
* Optimize set_node function to prevent triple lookup on contentfeatures
Do only one lookup for old, and try to merge old and new lookup if node is same than previous node
* Add benchmark function + optimize vector population to have real results
* Fix default item callbacks to work with nil users
* item.lua: Handle node drops for invalid players
The if-condition for the dropping loop is the same as `inv`, which means that the 2nd possible definition of `give_item` is never used.
Remove redundant `local _, dropped_item`
Implement network communication for channels
* Implement ModChannel manager server side to route incoming messages from clients to other clients
* Add signal handler switch on client & ModChannelMgr on client to handle channels
* Add Lua API bindings + client packet sending + unittests
* Implement server message sending
* Add callback from received message handler to Lua API using registration method
* Player attrs: permits to remove an attribute by setting value to nil
When doing player:set_attribute("attr", nil) remove attribute
Also remove a useless check on C++ API part (already done by checkplayer)
Fix#5709
"[sheet:WxH:X,Y" assumes the base image is a tilesheet with W*H tiles
on it and crops to the tile at position X,Y. Basically it works
like "[verticalframe" but in 2D.
For testing, I combined the four default_chest images into one.
Adds list-rings, a method to implement item sending between inventories via shift-click.
Nice insider feature: a ring consisting of a single inventory list serves as nice clean-up method.
Also adds them to minimal game, and the standard inventory.
Craft output slots are not supported.
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)
