if multiple canvases, don't auto-resize window to canvas size

[therewasaguy]

The changes from #132 (default sketch window size should be canvas size) make a big difference for the majority of projects.

But now, when working with instance mode / creating multiple canvases, the window resizes to only show the first canvas.

We could say that if we find more than one "createCanvas," do nothing / use default window size.