No FrameCount send over Spout.

[Kinggrass]

First of all thanks that this repos is existing and that you have put so much work into it.

We wanted to make use of it and unfortunatly it did not work like our other Spout senders (other applications/not unity).
We could track down that the issue is, that no frame counts are send and the receiving application does require it.

In particular https://spoutgl-site.netlify.app/#CClass:Spout:SetFrameCount should be respected where the sender should then send it.

I wanted to add it myself but after digging into this repo I found out that you are not using the Spout SDK but a self implemented light weight version.

Would it be possible to add this feature?

[Kinggrass]

@keijiro
I already solved my issue myself and I would like to provide a pull request: #100
If it will get merged or resolved in another way this issue can be closed.