Include MessagePort with event.data to remove a need to pass Events instances around

[Gozala]

This would address this TODO:

lunet/docs/lunet.js

Lines 54 to 56 in 84561e2

	// TODO: Fix up types. Problem is that we match on `data` which does not
	// refine event which is what we need to refine instead.
	const $event /*:any*/ = event

And also simplify bunch of code all around.

[Gozala]

It might be worth tackling this with #7 as later might render this obsolete or at least have some overlap.