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.

doc/lua_api.txt

@@ -1850,6 +1850,7 @@ Spatial Vectors
 * `vector.round(v)`: returns a vector, each dimension rounded to nearest int
 * `vector.apply(v, func)`: returns a vector
 * `vector.equals(v1, v2)`: returns a boolean
+* `vector.sort(v1, v2)`: returns minp, maxp vectors of the cuboid defined by v1 and v2
 
 For the following functions `x` can be either a vector or a number: