Organize builtin into subdirectories
Use "core" namespace internally
Fix healthbar not beeing hidden on disabled damage
Fix possible deadlock in error conditions
Fix error messages beeing shown on pressing cursor keys in various menus
Fix incorrect scaling of customized hud item selection marker
Fix invalid cast fix resulting in chat messages beeing limited to 256 bytes
Send max number of characters instead of asserting in case of too long chat messages
Merge remote-tracking branch 'minetest/master'

Conflicts:
	builtin/auth.lua
	builtin/builtin.lua
	builtin/chatcommands.lua
	builtin/game/falling.lua
	builtin/game/item.lua
	builtin/game/item_entity.lua
	builtin/misc.lua
	src/script/lua_api/l_env.cpp
	src/script/lua_api/l_env.h