Since the length of the data encoded by base58check affects the version
byte needed to produce a desired leading character, fix the length of
the payment code at 80 bytes, and correct the version byte to 0x23
Payment codes are SPV-friendly alternatives to DarkWallet-style stealth
addresses which provide useful features such as positively identifying
senders to recipients and automatically providing for transaction refunds.
Payment codes can be publicly advertised and associated with a real-life
identity without causing a loss of financial privacy.
Compared to stealth addresses, payment codes require less blockchain data
storage.
Payment codes require 65 bytes of OP_RETURN data per sender-recipient pair,
while stealth addresses require 40 bytes per transaction.
