Add vector helpers

doc/lua_api.txt

@@ -988,12 +988,41 @@ Inventory location:
 - "nodemeta:<X>,<Y>,<Z>": Any node metadata
 - "detached:<name>": A detached inventory
 
+Vector helpers
+---------------
+vector.new([x[, y, z]]) -> vector
+ ^ x is a table or the x position.
+vector.direction(p1, p2) -> vector
+vector.distance(p1, p2) -> number
+vector.length(v) -> number
+vector.normalize(v) -> vector
+vector.round(v) -> vector
+vector.equal(v1, v2) -> bool
+vector.add(v, x) -> vector
+ ^ x can be annother vector or a number
+vector.subtract(v, x) -> vector
+vector.multiply(v, x) -> vector
+vector.divide(v, x) -> vector
+
+You can also use Lua operators on vectors.
+For example:
+	v1 = vector.new()
+	v1 = v1 + 5
+	v2 = vector.new(v1)
+	v1 = v1 * v2
+	if v1 == v2 then
+		error("Math broke")
+	end
+
 Helper functions
 -----------------
 dump2(obj, name="_", dumped={})
 ^ Return object serialized as a string, handles reference loops
 dump(obj, dumped={})
 ^ Return object serialized as a string
+math.hypot(x, y)
+^ Get the hypotenuse of a triangle with legs x and y.
+  Usefull for distance calculation.
 string:split(separator)
 ^ eg. string:split("a,b", ",") == {"a","b"}
 string:trim()