Feature request: Additive frames

[corjohnson]

I'd love to be able to have additive lines be drawn as the frames continue to draw, but right now I'm not able to do that (or I don't really understand how to).

So if I draw a C in frame 1, in frame 2 I have to draw that same C in order to add to it.

Awesome tool!

[corjohnson]

Ah wait I see it's possible to do via selecting all frames, my bad!