Feature Request: add support GrainFactory3

[Dan64]

Hello Selur,

  I noted that in Hybrid there is only one grain filter: AddGrain. It would be useful add the support also to GrainFactory3 (in Vapoursynth is available in the library havsfunc).

This filter has a lot of parameter allowing more customization of the effect.

[Selur]

I'll look into it next week.

[Dan64]

Hello Selur,

   The development version with the new feature is working as expected.
   Thanks for having released this enhancement!