Support nomic-io/merk

[ethanfrey]

In order to demonstrate this proof format is generic (or adjust it as needed), we should add a new library to convert merk-js proofs (used by lotion.js) into this format, and add a number of test vectors to this repo.

This will be a unique, non-go Merkle tree implementation and should provide some learnings in making the format more flexible and generic

[ethanfrey]

Merk.js is gone, being replaced by merk.rs.

Implement this when the rust implementation is stable-ish.

[ethanfrey]

https://github.com/nomic-io/merk

[ethanfrey]

@mappum you want to take this over?