Big-Ugly Style Update (#278)

* Bulk replaced tabs with spaces
* Bulk removed trailing whitespace from lines
* Replaced c-style comments with c++-style comments in file banners
* Replace nested namespace definitions with single concise definitions (C++17), this keeps the indentation more manageable
* Cleanup ordering and spacing of include directives
* Bulk renaming of header file extensions from '.h' to '.hpp'.
* Update CODING-STYLE.md
* Update target_compile_features from cxx_std_11 to cxx_std_20.
* Refresh .clang-format file.  Still needs a lot of tweaking.

model/unit_tests/TestStrUtil.hpp

@@ -0,0 +1,31 @@
+//  TestColorNode.hpp
+//
+//  Copyright (C) 2019  Jaye Evins <evins@snaught.com>
+//
+//  This file is part of gLabels-qt.
+//
+//  gLabels-qt 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.
+//
+//  gLabels-qt 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 gLabels-qt.  If not, see <http://www.gnu.org/licenses/>.
+//
+
+
+#include <QtTest/QtTest>
+
+
+class TestStrUtil : public QObject
+{
+        Q_OBJECT
+
+private slots:
+        void formatFraction();
+};