Clarify what Proofmarshal is and write its specification

[gabridome]

To name "Proofmarshal" is not good if we have not a reference added as a footnote. Also it could be nice to add some notes on "single-use-seal" and “Proof-of-Publication-Ledgers”. I know only the blog post https://petertodd.org/2016/commitments-and-single-use-seals on the topic.

[dr-orlovsky]

I will post an original comment from Alekos roadmap here:

Proofmarshal: Design a protocol that would allow people to make RGB transactions without
going on-chain by asking a third-party, trustless, aggregator to commit to their proof along
with proofs from other people