bip322 support

[angrymouse]

Would be cool to see bcoin supporting bip322 signing/verifying.

[pinheadmz]

How widely adopted is that standard? I don't even think Bitcoin Core supports it yet. bcoin does sign with p2wpkh address though, I believe we conform to https://github.com/bitcoin/bips/blob/master/bip-0137.mediawiki