PlainKeychain
A really simple key-value wrapper for keychain.
Features
 kSecClassGenericPassword.
 kSecClassInternetPassword).
 
 kSecAttrAccessGroup.
Example
let keychain = PlainKeychain(service: "MyApp")
try keychain.setString("John", forKey: "nickname")
try keychain.getString(forKey: "nickname") // John
try keychain.deleteString(forKey: "nickname")