Add release notes for 0.5.22
# Release Notes
+## Changes in Splinter 0.5.22
+
+### Highlights
+
+* Experimental support for database-backed MerkleState in libscabbard has been
+ added.
+
+* Stabilize argument validation for internal services. This enables being able
+ to validate arbitrary service arguments in the admin service by defining
+ ServiceArgValidator for a service type. The admin service will run the
+ validator against a proposed circuit, rejecting a proposal if they are
+ invalid.
+
+### libsplinter
+
+* Stabilize `"service-arg-validation"` by removing the feature.
+
+* Fix type for admin service event ID for Postgres. The event ID was being set
+ to `INTEGER` but needs to be set to `BIGINT`.
+
+### splinterd
+
+* Stabilize `"service-arg-validation"` by removing the feature.
+
+* Add `scabbard_storage` configuration value. This value will allow splinterd to
+ enable the use of LMDB scabbard state. This value may be configured via
+ `splinterd.toml` or the `--scabbard-storage` CLI argument. This is behind the
+ experimental feature `"scabbard-database-support"`.
+
+### libscabbard
+
+* Stabilize `"service-arg-validation"` by removing the feature.
+
+* Stabilize `"receipt-store"` by removing the feature.
+
+* Enable the use of dynamic storage in the scabbard service, including the
+ `CommitHashStore` and the `ReceiptStore`. This is behind the experimental
+ feature `"database-support"`.
+
+* Enable the use of the transact library's `SqlMerkleState` in the scabbard
+ service, with LMDB as an optional alternative. This is behind the experimental
+ feature `"database-support"`.
+
+* Fix the `dir_path` arg given when creating a new `LmdbReceiptStore`.
+ Previously the value given for this argument included the name of the LMDB
+ file in the path which caused an error.
+
+* Fix receipt store configuration in scabbard. Previously, this was setting the
+ wrong value, resulting in the receipt-store configuration to be the default
+ values.
+
+* Consolidate scabbard migrations, by including transact and sawtooth migration
+ execution under the scabbard migration functions. This removes the need for
+ library consumers to use either of those libraries and prevents situations
+ where the database might be only partially migrated for scabbard's purposes.
+
## Changes in Splinter 0.5.21
### Highlights
