This module is for generating ack payload
Generate and return payload obj.
This function generates payload objects for message acknowledgements Several stealth levels are available depending on the privacy needs; a higher level means better stealth, but also higher cost (size+POW)
- level 0: a random 32-byte sequence with a message header appended
- level 1: a getpubkey request for a (random) dummy key hash
- level 2: a standard message, encrypted to a random pubkey