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

src/catch2/catch_test_case_tracker.cpp

@@ -5,10 +5,10 @@
  *  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  */
 
-#include "catch_test_case_tracker.h"
+#include <catch2/catch_test_case_tracker.h>
 
-#include "catch_enforce.h"
-#include "catch_string_manip.h"
+#include <catch2/catch_enforce.h>
+#include <catch2/catch_string_manip.h>
 
 #include <algorithm>
 #include <cassert>