Rewrite includes inside the library to use <catch2/> form

src/catch2/catch_session.h

@@ -8,9 +8,9 @@
 #ifndef TWOBLUECUBES_CATCH_RUNNER_HPP_INCLUDED
 #define TWOBLUECUBES_CATCH_RUNNER_HPP_INCLUDED
 
-#include "catch_commandline.h"
-#include "catch_config.hpp"
-#include "catch_text.h"
+#include <catch2/catch_commandline.h>
+#include <catch2/catch_config.hpp>
+#include <catch2/catch_text.h>
 
 #include <memory>