Mbin support

I'm thinking of creating a PR to replace the client used in Lemmy Federate with this library. However, the lack of Mbin support is not backwards compatible. I'd like to create a PR for this library, but I don't have time to implement the entire Mbin. Would it be sufficient to just add the features required by Lemmy Federate?

It's just 3 methods and an interface: https://github.com/Fedihosting-Foundation-Forks/lemmy-federate/blob/main/src/types/LFClient.ts

cc @MrKaplan-lw @aeharding