* Update go-secp256k1 to v0.0.3
* Update the txscript engine to support only 32 bytes pubkeys
* Update the txscript engine tests
* Update txscript/sign.go to use the new Schnorr KeyPair API
* Update txscript sign_test to use the new schnorr
* Update sigcache tests to use new schnorr pubkey
* Update integration tests to use the new txscript and new schnorr pubkey