Clean-up and XML handling enhancement:

- XML helper functions always return objects by winstd::com_obj or winstd::bstr reference now to ensure proper release by caller
- get_element_value()/put_element_value() can optionally return reference to the XML object if required
- WinStd macros to simplify dplhandle<> and handle<> inherited classes reused by non-copyable classes

lib/TLS/src/Method.cpp

@@ -223,7 +223,7 @@ void eap::method_tls::begin_session(
     }
 
     // Prepare client credentials for Schannel.
-    PCCERT_CONTEXT certs[] = { m_cred.m_cert ? m_cred.m_cert : NULL };
+    PCCERT_CONTEXT certs[] = { m_cred.m_cert ? (PCCERT_CONTEXT)m_cred.m_cert : NULL };
     SCHANNEL_CRED cred = {
         SCHANNEL_CRED_VERSION,                                                // dwVersion
         m_cred.m_cert ? 1 : 0,                                                // cCreds