Make util::not_implemented throw a specific exception type instead of runtime_error

libs/util/include/psemek/util/not_implemented.hpp

@@ -1,8 +1,16 @@
 #pragma once
 
+#include <exception>
+
 namespace psemek::util
 {
 
+	struct not_implemented_error
+		: std::exception
+	{
+		char const * what() const noexcept override;
+	};
+
 	[[noreturn]] void not_implemented();
 
 }

libs/util/source/not_implemented.cpp

@@ -5,9 +5,14 @@
 namespace psemek::util
 {
 
+	char const * not_implemented_error::what() const noexcept
+	{
+		return "not implemented";
+	}
+
 	void not_implemented()
 	{
-		throw std::runtime_error("Not implemented");
+		throw not_implemented_error{};
 	}
 
 }