MSIGN function creates a cryptographic signature of a macro. The cryptographic signature is itself a macro with the following structure:
<% 'CURVE' 'PUBKEY' 'SIG' MSIG %>
CURVE is the name of the Elliptic Curve Cryptography to use,
PUBKEY is the hex encoded public key (
Q parameter) which can be used to verify the signature and
SIG is the hex encoded
SHA256WITHECSDA signature of the
UTF-8 content of the snapshot of the macro.