Don't hardcode ver, update node name, and add tests

src/xmpp/hash_disco.hpp

@@ -0,0 +1,16 @@
+#pragma once
+
+#include <xmpp/xmpp_stanza.hpp>
+
+namespace Xmpp
+{
+  /**
+   * Generate a verification string according to XEP-0115
+   * https://xmpp.org/extensions/xep-0115.html#ver
+   *
+   * This does NOT support Service Discovery Extensions (XEP-0128).
+   * Nor does this sort identities by language
+   */
+  const std::string hash_disco_sha1(const Stanza &stanza);
+}
+