Port to CMake from qmake, and split decoder into subdirectory

Qt 5 has had to be dropped as CMakeLists.txt uses qt_* specific commands
which are implemented in Qt 6 onwards.

cmake --install is only working on Linux at the moment; it installs the
executable and the bundled example tti files into /usr/local/share/doc

The teletext decoder with its document storage has been moved to a
subdirectory with the intention of making it possible to use in other
projects, but some further separation of editing stuff will be needed.

src/qteletextmaker/main.cpp

@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2020-2024 Gavin MacGregor
+ *
+ * This file is part of QTeletextMaker.
+ *
+ * QTeletextMaker 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 of the License, or
+ * (at your option) any later version.
+ *
+ * QTeletextMaker 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 QTeletextMaker.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <QApplication>
+#include <QCommandLineParser>
+
+#include "mainwindow.h"
+
+int main(int argc, char *argv[])
+{
+	Q_INIT_RESOURCE(actionicons);
+	QApplication app(argc, argv);
+	QApplication::setApplicationName("QTeletextMaker");
+	QApplication::setApplicationDisplayName(QApplication::applicationName());
+	QApplication::setOrganizationName("gkmac.co.uk");
+	QApplication::setOrganizationDomain("gkmac.co.uk");
+	QApplication::setApplicationVersion("0.6.4-beta");
+	QCommandLineParser parser;
+	parser.setApplicationDescription(QApplication::applicationName());
+	parser.addHelpOption();
+	parser.addVersionOption();
+	parser.addPositionalArgument("file", "The file(s) to open.");
+	parser.process(app);
+
+	MainWindow *mainWin = Q_NULLPTR;
+	foreach (const QString &file, parser.positionalArguments()) {
+		MainWindow *newWin = new MainWindow(file);
+		newWin->tile(mainWin);
+		newWin->show();
+		mainWin = newWin;
+	}
+
+	if (!mainWin)
+		mainWin = new MainWindow;
+	mainWin->show();
+
+	return app.exec();
+}