mu-message-field: Implement

Implement Mu::MessageField, which replace MuMsgField with something a bit more
modern.

lib/mu-message.hh

@@ -0,0 +1,40 @@
+/*
+** Copyright (C) 2022 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
+**
+** This program is free software; you can redistribute it and/or modify it
+** under the terms of the GNU General Public License as published by the
+** Free Software Foundation; either version 3, or (at your option) any
+** later version.
+**
+** This program is distributed in the hope that it will be useful,
+** but WITHOUT ANY WARRANTY; without even the implied warranty of
+** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+** GNU General Public License for more details.
+**
+** You should have received a copy of the GNU General Public License
+** along with this program; if not, write to the Free Software Foundation,
+** Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+**
+*/
+
+#ifndef MU_MESSAGE_HH__
+#define MU_MESSAGE_HH__
+
+#include "mu-message-contact.hh"
+#include "mu-message-priority.hh"
+#include "mu-message-flags.hh"
+#include "mu-message-fields.hh"
+
+namespace Mu {
+
+namespace Message {
+
+using   Contact  = MessageContact;
+using   Contacts = MessageContacts;
+using	Priority = MessagePriority;
+using	Flags	 = MessageFlags;
+using	Field	 = MessageField;
+
+} // Message
+} // Mu
+#endif /* MU_MESSAGE_HH__ */