Start using piecemeal includes in test files

tests/SelfTest/UsageTests/Matchers.tests.cpp

@@ -1,15 +1,18 @@
 /*
- *  Created by Phil on 21/02/2017.
- *  Copyright 2017 Two Blue Cubes Ltd. All rights reserved.
- *
  *  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 <catch2/catch.hpp>
+#include <catch2/catch_test_macros.hpp>
+#include <catch2/catch_matchers_exception.hpp>
+#include <catch2/catch_matchers_floating.h>
+#include <catch2/catch_matchers_generic.hpp>
+#include <catch2/catch_matchers_string.h>
+#include <catch2/catch_matchers_vector.h>
 
 #include <sstream>
 #include <algorithm>
+#include <cmath>
 
 #ifdef __clang__
 #pragma clang diagnostic push