add signmessage and verifymessage
reuse Bitcoin.bitcoin_signed_message_hash in  Bitcoin::Key#recover_public_key_from_signature
improve Script#get_address parsing for non-standard OP_CHECKMULTISIG
backward compatible change for on_verack
fix script opcode parsing edge case

  found in testnet3 tx: 5dea81f9d9d2ea6d06ce23ff225d1e240392519017643f75c96fa2e4316d948a

  there are no two bye opcodes and i don't recall why it was added back then.
Merge branch 'master' of https://github.com/lian/bitcoin-ruby