Remove functions which are deprecated and which I do not recommend to use

Removing deprecated functionality can help to clean up the code a bit.

I remove the following deprecated functions and values:
* vector.zero
* vector.plane()
* vector.pos_to_string()
* vector.quickadd()
* vector.scalar()
* vector.get_data_from_pos()
* vector.set_data_to_pos()
* vector.set_data_to_pos_optional()
* vector.remove_data_from_pos()
* vector.get_data_pos_table()

Furthermore, I remove the unused, experimental vector_meta.lua file
and make luacheck linting more strict so that it can show accidental
uses of deprecated functions in the code of this mod if there are any.

This change can break compatility with old mods which use vector_extras.

init.lua

@@ -2,10 +2,6 @@ local path = minetest.get_modpath"vector_extras"
 
 local funcs = {}
 
-function funcs.pos_to_string(pos)
-	return "("..pos.x.."|"..pos.y.."|"..pos.z..")"
-end
-
 local r_corr = 0.25 --remove a bit more nodes (if shooting diagonal) to let it
 -- look like a hole (sth like antialiasing)
 
@@ -270,63 +266,6 @@ function funcs.pnorm(v, p)
 	return (math.abs(v.x)^p + math.abs(v.y)^p + math.abs(v.z)^p)^(1 / p)
 end
 
---not optimized
---local areas = {}
-function funcs.plane(ps)
-	-- sort positions and imagine the first one (A) as vector.zero
-	vector.sort_positions(ps)
-	local pos = ps[1]
-	local B = vector.subtract(ps[2], pos)
-	local C = vector.subtract(ps[3], pos)
-
-	-- get the positions for the fors
-	local cube_p1 = {x=0, y=0, z=0}
-	local cube_p2 = {x=0, y=0, z=0}
-	for i in pairs(cube_p1) do
-		cube_p1[i] = math.min(B[i], C[i], 0)
-		cube_p2[i] = math.max(B[i], C[i], 0)
-	end
-	cube_p1 = vector.apply(cube_p1, math.floor)
-	cube_p2 = vector.apply(cube_p2, math.ceil)
-
-	local vn = vector.normalize(vector.cross(B, C))
-
-	local nAB = vector.normalize(B)
-	local nAC = vector.normalize(C)
-	local angle_BAC = math.acos(vector.dot(nAB, nAC))
-
-	local nBA = vector.multiply(nAB, -1)
-	local nBC = vector.normalize(vector.subtract(C, B))
-	local angle_ABC = math.acos(vector.dot(nBA, nBC))
-
-	for z = cube_p1.z, cube_p2.z do
-		for y = cube_p1.y, cube_p2.y do
-			for x = cube_p1.x, cube_p2.x do
-				local p = {x=x, y=y, z=z}
-				local n = -vector.dot(p, vn)/vector.dot(vn, vn)
-				if math.abs(n) <= 0.5 then
-					local ep = vector.add(p, vector.multiply(vn, n))
-					local nep = vector.normalize(ep)
-					local angle_BAep = math.acos(vector.dot(nAB, nep))
-					local angle_CAep = math.acos(vector.dot(nAC, nep))
-					local angldif = angle_BAC - (angle_BAep+angle_CAep)
-					if math.abs(angldif) < 0.001 then
-						ep = vector.subtract(ep, B)
-						nep = vector.normalize(ep)
-						local angle_ABep = math.acos(vector.dot(nBA, nep))
-						local angle_CBep = math.acos(vector.dot(nBC, nep))
-						angldif = angle_ABC - (angle_ABep+angle_CBep)
-						if math.abs(angldif) < 0.001 then
-							table.insert(ps, vector.add(pos, p))
-						end
-					end
-				end
-			end
-		end
-	end
-	return ps
-end
-
 function funcs.straightdelay(s, v, a)
 	if not a then
 		return s/v
@@ -334,17 +273,6 @@ function funcs.straightdelay(s, v, a)
 	return (math.sqrt(v*v+2*a*s)-v)/a
 end
 
--- override vector.zero
--- builtin used not to have the vector.zero function. to keep compatibility,
--- vector.zero has to be a 0-vector and vector.zero() has to return a 0-vector
--- => we make a callable 0-vector table
-if not vector.zero then
-	vector.zero = {x = 0, y = 0, z = 0}
-else
-	local old_zero = vector.zero
-	vector.zero = setmetatable({x = 0, y = 0, z = 0}, {__call = old_zero})
-end
-
 function funcs.sun_dir(time)
 	if not time then
 		time = minetest.get_timeofday()
@@ -901,18 +829,6 @@ function funcs.update_minp_maxp(minp, maxp, pos)
 	end
 end
 
-function funcs.quickadd(pos, z,y,x)
-	if z then
-		pos.z = pos.z+z
-	end
-	if y then
-		pos.y = pos.y+y
-	end
-	if x then
-		pos.x = pos.x+x
-	end
-end
-
 function funcs.unpack(pos)
 	return pos.z, pos.y, pos.x
 end
@@ -1021,20 +937,12 @@ function funcs.triangle(pos1, pos2, pos3)
 	return points, n, barycentric_coords
 end
 
-
-vector_extras_functions = funcs
-
-dofile(path .. "/legacy.lua")
---dofile(minetest.get_modpath("vector_extras").."/vector_meta.lua")
-
-vector_extras_functions = nil
-
-
 for name,func in pairs(funcs) do
 	if vector[name] then
 		minetest.log("error", "[vector_extras] vector."..name..
 			" already exists.")
 	else
+		-- luacheck: globals vector
 		vector[name] = func
 	end
 end