This is a more generic version of `keychain::persist::*` structures. Additional changes: * The `Append` trait has a new method `is_empty`. * Introduce `Store` structure for `bdk_file_store`.
BDK File Store
This is a simple append-only flat file implementation of
Persist.
The main structure is KeychainStore, which can be used with bdk's
Wallet to persist wallet data into a flat file.