Cashu Nutshell v0.12.3: Pay To Pubkey (P2PK)

- "This Nutshell release introduces a new token lock type called Pay-to-Pubkey or P2PK.

- "This allows you to create ecash tokens that can only be spent by their designated recipient. A token locked with P2PK can be posted online without any third party being able to spend it."

- "In an upcoming upgrade we will also add DLEQ proofs (PR) which allow anyone to check the validity of the mint's signature on a token without having to contact the mint."

- "These two features combined, P2PK and DLEQ proofs, allow for a very interesting use case: publicly verifiable payments to a pubkey in the form of ecash."