Allow user defined ioctl

This expose  `_IO*` functions in `ioctl` module to allow users to define any not yet defined ioctl.

BTW, here is the ioctls that I needed to define (to create a uinput device) if you want to add them too:

```lua
UI_DEV_CREATE  = _IO ('U',   1)
UI_DEV_DESTROY = _IO ('U',   2)
UI_SET_EVBIT   = _IOW('U', 100, s.int)
UI_SET_KEYBIT  = _IOW('U', 101, s.int)
```