Add useLayoutEffect

[matthewp]

This is used to synchronously cause an effect directly after rendering. This could be useful for doing adoptedStylesheets stuff.

[justinfagnani]

What would this correspond to in the custom element lifecycle?

[matthewp]

Likely this would happen immediately after render(templateResult) is called.

[justinfagnani]

How would this work with LitElement integration? Should LitElement callback into Haunted in updated()?

[matthewp]

With the new State API there's a state.callEffects() for useEffect hooks, so I imagine something similar would be added for this.

[cletusw]

Fixed by #136 ?