Add regex search, search/replace, and buffer read-only mode functionality with help text

HelpText.h

@@ -0,0 +1,17 @@
+/*
+ * HelpText.h - embedded/customizable help content
+ */
+#ifndef KTE_HELPTEXT_H
+#define KTE_HELPTEXT_H
+
+#include <string>
+
+class HelpText {
+public:
+    // Returns the embedded help text as a single string with newlines.
+    // Project maintainers can customize the returned string below
+    // (in HelpText.cc) without touching the help command logic.
+    static std::string Text();
+};
+
+#endif // KTE_HELPTEXT_H