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

src/catch2/catch_context.cpp

@@ -5,9 +5,9 @@
  *  Distributed under the Boost Software License, Version 1.0. (See accompanying
  *  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  */
-#include "catch_context.h"
-#include "catch_common.h"
-#include "catch_random_number_generator.h"
+#include <catch2/catch_context.h>
+#include <catch2/catch_common.h>
+#include <catch2/catch_random_number_generator.h>
 
 namespace Catch {