Use OpenPGP keys for signing

To sign the data with OpenPGP keys, you need to employ TElXMLKeyInfoPGPData class. All you need to do is

1. Create an instance of TElXMLKeyInfoPGPData class.
2. Load the OpenPGP secret key to the instance of TElPGPSecretKey class.
3. Set the passphrase for the secret key to Passphrase property of TElXMLKeyInfoPGPData class.
4. Set the loaded key to SecretKey property of TElXMLKeyInfoPGPData class. Note, that the original object is set. No copy is made.
5. Set KeyData property of TElXMLSigner to the instance of TElXMLKeyInfoPGPData class which contains the key.