refactor: switch to async iterators

[vasco-santos]

BREAKING CHANGE: Switch to using async/await and async iterators.

Needs

• libp2p/js-libp2p-pubsub#26

[vasco-santos]

As the example was not even complete and we already have a pubsub example on js-libp2p, I think that it is not worth to have another one to maintain here.

Ideally, we should look at https://github.com/libp2p/js-libp2p-examples as the way to go? Once I get to automation of the interop for js-libp2p, I will also look into adding CI jobs for examples and we should probably migrate all examples to there and like in the appropriate repos the examples

[jacobheun]

Some minor feedback right now. The majority of feedback for the pubsub PRs is in the abstract module, libp2p/js-libp2p-pubsub#26. I also left comments that will affect this in the js-libp2p PR libp2p/js-libp2p#467

[jacobheun]

One minor thing but otherwise this looks good. Just a friendly reminder to release as a beta dist-tag when it's ready :)

[jacobheun]

Should we just remove the registrar declaration here and make node that it is a libp2p Registrar? I know we don't have the docs flushed out for that yet, but we can point to that once it's done.

[vasco-santos]

I think you are right! Added a comment and removed the declaration. Once we have the docs, I will add a pointer to them here