Implement VoxelArea

[TurkeyMcMac]

Closes #34.

This is an independent VoxelArea implementation. There are tests.

[S-S-X]

Implementation has to be moved to root directory.

Reason why this cannot be in game directory is because it is not coming from core engine lua scripts.
game directory for different engine versions gets populated from git minetest engine git repo, there should not be anything but unmodified minetest core engine lua scripts.

[TurkeyMcMac]

Perhaps you could just copy the implementation from Minetest and put it in the game/ directory.

[S-S-X]

Perhaps you could just copy the implementation from Minetest and put it in the game/ directory.

Actually I think It'll be available if you run Mineunit with full Minetest core libraries using for example

mineunit --fetch-core 5.5.0 --engine-version 5.5.0

Everything around engine core libs is just badly messed up... that's mostly because it was not planned in any way and added on top of messed up directory structure.

See this crap for example:

mineunit/init.lua

Lines 52 to 71 in db70bcd

	local function require_mineunit(name, root, tag)
	local modulename = name:gsub("/", ".")
	if root and tag and tag ~= "mineunit" then
	local path = name:match("^([^/]+)/")
	if path and tagged_paths[path] then
	local oldpath = package.path
	local module
	package.path = root.."/"..tag.."/?.lua;"
	mineunit:debug("Loading "..name.." from "..tag)
	local success = pcall(function() module = require(modulename)end)
	package.path = oldpath
	if success then
	return module
	else
	mineunit:error("Loading "..name.." from "..tag.." failed, trying to use builtin")
	end
	end
	end
	return require("mineunit." .. modulename)
	end

Engine core library management requires some serious refactoring and I've planned to do that at some point in future but probably before that I have to refactor another completely messed up thing which is current Mineunit configuration system.

[S-S-X]

Tested VoxelArea using --engine-version 5.4.1 mt-mods/technic@385ce5b
Seems to work fine.

• Related Technic PR: Use node timers to spread out LV lamp updates mt-mods/technic#291

However that's not really fixing whole issue as core library version management is still terrible.
I think it would be best to include some "default" VoxelArea with Mineunit, decision is mostly between including VoxelArea library direct from engine or going with this PR.

[TurkeyMcMac]

I suppose it depends on the license of Minetest's implementation.

[S-S-X]

LGPL 2.1 which is fine and already included here too https://github.com/S-S-X/mineunit/blob/master/LICENSE because there's few libraries included as is without changes directly from Minetest.
I did go through licensing when I was about to add core libs, determined that licenses are compatible and libraries can be included.