Vector: Add vector.sort(a, b): return box edges

This function returns the box corners of the smallest box
that includes the two given coordinates.

builtin/common/vector.lua

@@ -138,3 +138,8 @@ function vector.divide(a, b)
 			z = a.z / b}
 	end
 end
+
+function vector.sort(a, b)
+	return {x = math.min(a.x, b.x), y = math.min(a.y, b.y), z = math.min(a.z, b.z)},
+		{x = math.max(a.x, b.x), y = math.max(a.y, b.y), z = math.max(a.z, b.z)}
+end