Convert digilines to a mod (not modpack). (#32)

Digilines is probably used by most people in its entirety.

I've retained the ability to disable inventory, rtc, lightsensor and
LCD by the minetest settings "diglines_enable_rtc" etc.. If set to
"false", these components will not be loaded. It is assumed by default
that these are enabled.

In the conversion the digilines_lcd:lcd node was renamed to
digilines:lcd (same for all the other nodes). To retain backwards
compatibility I've provided aliases for each of these nodes.

util.lua

@@ -0,0 +1,67 @@
+function digiline:addPosRule(p, r)
+	return {x = p.x + r.x, y = p.y + r.y, z = p.z + r.z}
+end
+
+function digiline:cmpPos(p1, p2)
+	return (p1.x == p2.x and p1.y == p2.y and p1.z == p2.z)
+end
+
+--Rules rotation Functions:
+function digiline:rotate_rules_right(rules)
+	local nr={}
+	for i, rule in ipairs(rules) do
+		nr[i]={}
+		nr[i].z=rule.x
+		nr[i].x=-rule.z
+		nr[i].y=rule.y
+	end
+	return nr
+end
+
+function digiline:rotate_rules_left(rules)
+	local nr={}
+	for i, rule in ipairs(rules) do
+		nr[i]={}
+		nr[i].z=-rules[i].x
+		nr[i].x=rules[i].z
+		nr[i].y=rules[i].y
+	end
+	return nr
+end
+
+function digiline:rotate_rules_down(rules)
+	local nr={}
+	for i, rule in ipairs(rules) do
+		nr[i]={}
+		nr[i].y=rule.x
+		nr[i].x=-rule.y
+		nr[i].z=rule.z
+	end
+	return nr
+end
+
+function digiline:rotate_rules_up(rules)
+	local nr={}
+	for i, rule in ipairs(rules) do
+		nr[i]={}
+		nr[i].y=-rule.x
+		nr[i].x=rule.y
+		nr[i].z=rule.z
+	end
+	return nr
+end
+
+function digiline:tablecopy(table) -- deep table copy
+	if type(table) ~= "table" then return table end -- no need to copy
+	local newtable = {}
+
+	for idx, item in pairs(table) do
+		if type(item) == "table" then
+			newtable[idx] = digiline:tablecopy(item)
+		else
+			newtable[idx] = item
+		end
+	end
+
+	return newtable
+end