Big assertion capture refactoring.

- moved as much logic out of the macros as possible
- moved most logic into new ResultBuilder class, which wraps ExpressionResultBuilder (may take it over next), subsumes ResultAction and also takes place of ExpressionDecomposer.

This introduces many SRP violations - but all in the name of minimising macro logic!

include/internal/catch_impl.hpp

@@ -34,6 +34,7 @@
 #include "catch_section.hpp"
 #include "catch_debugger.hpp"
 #include "catch_tostring.hpp"
+#include "catch_result_builder.hpp"
 
 #include "../reporters/catch_reporter_xml.hpp"
 #include "../reporters/catch_reporter_junit.hpp"