Streamline includes in external interfaces

include/internal/catch_config.hpp

@@ -9,9 +9,7 @@
 #define TWOBLUECUBES_CATCH_CONFIG_HPP_INCLUDED
 
 #include "catch_test_spec_parser.hpp"
-#include "catch_context.h"
 #include "catch_interfaces_config.h"
-#include "catch_stream.h"
 
 #include <memory>
 #include <vector>
@@ -23,6 +21,8 @@
 
 namespace Catch {
 
+    struct IStream;
+
     struct ConfigData {
         bool listTests = false;
         bool listTags = false;