Client management

• Download NDF.
• Generate a secure password.
• Handle secure password storage with the iOS keychain.
• Create and store a new client.
• Load stored client.
• Remove stored client.
• Example app with all of the above.

Sources/ElixxirDAppsSDK/Errors.swift

+public struct BindingsDownloadAndVerifySignedNdfWithUrlUnknownError: Error, Equatable {
+  public init() {}
+}