IMPORTANT: This is a protocol upgrade so you must update to be
compatible with the network.
https://github.com/stellar/stellar-core/releases
# New Features
- bumped the protocol version
- [New signing
types](https://www.stellar.org/developers/guides/concepts/multi-sig.html#alternate-signature-types)
- hash(x)
- pre-authorized transaction
- added `PREFERRED_UPGRADE_DATETIME` as an optional .cfg parameter.
Allows the network to better coordinate an upgrade date.
- `--signtxn` now allows you to specify network to sign for
- improved error messages
# Fixes
- orderbook issue
- speeds up and more reliable catchup
- small bug fixes
- stability improvements
