T3060
Per the updated alias spec, alias registration txs will have the following format
`6a` - OP_RETURN
`04` - 4 bytes pushdata
`2e786563` - alias protocol identifier (".xec")
`01` - alias protocol version number pushdata
`00` - alias protocol version number
`**` - 1 byte pushdata, alias.length, in hex, e.g. '04' for a 4-byte alias registration, a value between `0x01` and `0x15`
`********` - n bytes, alias in hex
`15` - 21 bytes of pushdata for address and address version byte
`00` or `08` - marks address as p2pkh or p2sh
`<hash>` - address payload
A new function `generateAliasOpReturnScript` is added to create an OP_RETURN script matching this spec. Unit tests are added for sample registrations to p2pkh and p2sh addresses.