Warn when `toString` behavior will be different.

[Gozala]

js-multiformats introduced more deterministic behavior of toString() method which could lead to a different behavior in comparison to .toString() method here.

We should amend .toString() method implementation here to print a warning in instances where behavior exhibited by js-multiformats would defer and provide a link to migration guide.

[Gozala]

@mikeal I've assigned it to you because I think you're only one who actually understands this.

[Gozala]

I think we should make sure that warning printed is actionable in some way e.g. users can opt-in into future behavior otherwise it's just going to be annoyance.