Added KeyringControllerPersistentState type which includes only persistent state, an optional string property with key vault (#247)
Added KeyringObject type for how keyrings are represented in memStore (#247)

Changed

BREAKING: Add types for store and fix type discrepancies (#247)
BREAKING: Constructor parameter KeyringControllerArgs fields changed (#247):
BREAKING: type of store and memStore public properties changed (#247):
- KeyringController.store is now an ObservableStore<KeyringControllerPersistentState>
- KeyringController.memStore is now an ObservableStore<KeyringControllerState>
BREAKING: updateMemStoreKeyrings method return type changed to Promise<void> (#247)
BREAKING: KeyringControllerState type changed to include only non-persistent state (#247):
- Now undefined is used instead of null when encryptionKey and encryptionSalt are unset
- keyrings is now of type KeyringObject[] instead of Keyring<Json>
- password, store, memStore have been removed - note that in practice this change only affects types
- This changes cause the following methods also to change the return type:
  - createNewVaultAndKeychain
  - createNewVaultAndRestore
  - setLocked
  - submitPassword
  - submitEncryptionKey
  - addNewAccount
  - removeAccount
  - fullUpdate
BREAKING: When constructing a simple keyring with addNewKeyring, the second parameter (opts) is now expected to be an array of private keys rather than an object with a privateKeys property (#253)
Restored support for keyrings with non-object serialized state (#253)
Narrow return type of signTypedMessage and encryption methods (#249)
- The methods signTypedMessage, getEncryptionPublicKey, and decryptMessage now return string rather than Bytes

Fixed

Fix signTypedMessage parameter types (#250)
Restore compatibility with QR Keyring (#252)
- An empty object is no longer used as a default when deserialized state was not provided to the addNewKeyring method. This default empty object was breaking the QR keyring.