====== spawnProjectileByDir ======
  * Parameters and types:
     * shooter: numberSet the objid to which the thrown object belongs
    * itemid: numberthrowable id
     * x,y,z: numberstarting point of the thrown object
     * dstx, dsty, dstz: numberthrowing direction
    * speed: numberThrowing speed
  * Return value and type:
     * code: numberSuccess (ErrorCode.OK) ErrorCode
    * objid: numberThe instance ID of the thrown object
  * The main purpose of this method: Generate projectiles (by direction)
  * The specific use cases are as follows:

<code>
local code, objid = World:spawnProjectileByDir(shooter, itemid, x, y, z, dirx, diry, dirz, speed)
if code == ErrorCode.OK then
print('Execution success', code, objid )
else
print('Execution failure')
end
</code>