Addroom (x, y, z)

   Synopsis:
      Adds a new room near the automapper's current room

   Notes:
      The three arguments are the coordinates of the gridblock, relative to the
         automapper's current room, at which the new room will be drawn.
      If the operation is successful, the new room's world model number is
         returned. If there is no current room, if the coordinates x, y and z
         are invalid, if the gridblock is already occupied or if the operation
         fails, 0 is returned.
      See also the Addfirstroom () function.

   Examples:
      Addroom (1, 2, 0)    >> Adds a room one block below and two blocks to the
                              right of the current room
      Addroom (-3, -4, 0)  >> Adds a room three blocks above and four blocks to
                              the left of the current room
      Addroom (0, 0, 1)    >> Adds a room one level higher than the current room
      Addroom (0, 0, -2)   >> Adds a room two levels lower than the current room
