`useRefs` Hook

[rimuy]

Linked to #17

[rimuy]

Also accomplishes what seems it should've been possible from the beginning: https://github.com/evaera/plasma/blob/615632409813feb2d74f4d88f1f99ee01c8786bb/src/create.lua#L41-L54

[rimuy]

There's not really an alternative here, it's either this or giving the user a way to set the current node.refs via some function, the behavior of erroring outside useInstance should still stay. It still makes more sense just returning the table so users could do that manually.