Issue #24 Created PublicKey and PublicKeys interfaces.
Issue #24 Added RtPublicKey and RtPublicKeyTest.
Issue #24 Added RtPublicKeys, RtPublicKeysITCase, RtPublicKeysTest.
Issue #24 Added MkPublicKey, MkPublicKeys, MkPublicKeyTest,
MkPublicKeyTests classes. Added User.key() method.