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.

glbarcode/Constants.hpp

@@ -0,0 +1,38 @@
+//  Constants.hpp
+//
+//  Copyright (C) 2013  Jaye Evins <evins@snaught.com>
+//
+//  This file is part of glbarcode++.
+//
+//  glbarcode++ is free software: you can redistribute it and/or modify
+//  it under the terms of the GNU Lesser General Public License as published by
+//  the Free Software Foundation, either version 3 of the License, or
+//  (at your option) any later version.
+//
+//  glbarcode++ 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 Lesser General Public License for more details.
+//
+//  You should have received a copy of the GNU Lesser General Public License
+//  along with glbarcode++.  If not, see <http://www.gnu.org/licenses/>.
+//
+
+#ifndef glbarcode_Constants_hpp
+#define glbarcode_Constants_hpp
+
+
+namespace glbarcode
+{
+
+        namespace Constants
+        {
+                const double PTS_PER_INCH = 72.0;            /**< Points per inch. */
+                const double PTS_PER_MM   =  2.83464566929;  /**< Points per millimeter. */
+                const double PTS_PER_CM   = 10*PTS_PER_MM;   /**< Points per centimeter. */
+        }
+
+}
+
+
+#endif // glbarcode_Constants_hpp