Add commit 43aab01 of BenHanson/lexertl14 from github

YACReaderLibrary/lexertl/char_traits.hpp

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+// char_traits.hpp
+// Copyright (c) 2005-2018 Ben Hanson (http://www.benhanson.net/)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file licence_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef LEXERTL_CHAR_TRAITS_HPP
+#define LEXERTL_CHAR_TRAITS_HPP
+
+#include <cstddef>
+
+namespace lexertl
+{
+template<typename ch_type>
+struct basic_char_traits
+{
+    using char_type = ch_type;
+    using index_type = ch_type;
+
+    static index_type max_val()
+    {
+        const std::uint32_t max_ = 0x10ffff;
+
+        return sizeof(char_type) > 2 ?
+            max_ : (max_ & 0xffff);
+    }
+};
+
+template<>
+struct basic_char_traits<char>
+{
+    using char_type = char;
+    using index_type = unsigned char;
+
+    static index_type max_val()
+    {
+        // Prevent annoying warning (VC++)
+        index_type zero_ = 0;
+
+        return ~zero_;
+    }
+};
+}
+
+#endif