Knob grouping

[pollend]

It would be nice to able to create subgroups of knobs. I've abstracted this out on my end but it would be a nice feature to see in a future release of the library.

[Seneral]

Just to be sure, what would these subgroups be for? Visual grouping of normal knobs, or do they have their dedicated structure/API?
If it's the first, it wouldn't need structural grouping, a function to draw knob x-y together would suffice, right?
Also, if you feel comfortable don't hesitate to make a PR with your work on this;)

[pollend]

So the way you restore canvases is to duplicate all objects and this ends up breaking any references to that knob. It would be nice to subgroup nodes so you only have to track the subgroups of knobs rather then the entire set. It's not too bad to work around this limitation but its pretty fiddly. This is what i can gather from looking through the code. I may be wrong but I'm pretty sure that is what is happening.

In terms of implementing, I'm not sure how this would work out. It seems a bit complicated to implement.

[Seneral]

Oh, so there's actually a better way to approach this problem. I'm imagining attributes to tag these references and then restoring those are automatically handled.
Also, reminds me of #91 ;)
I'll adress this Problem soon!