Add AutoLayout (cassowary) option

[andydotxyz]

Add a Cassowary algorithm to create an AutoLayout setup. A slice of Constraints should likely exist within the CanvasObject to facilitate the layout.

[xlab]

Sorry maybe totally unrelated, but can Flex be integrated too https://github.com/kjk/flex ?
I hoped that algorithms for "auto layout" can be swapped using some common interface.

[andydotxyz]

I think #47 may be what you’re looking for @xlab .

I doubt we can do this with a common interface as they use very different metadata.