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_common.h

@@ -94,6 +94,8 @@ namespace Catch {
 
     // This is just here to avoid compiler warnings with macro constants and boolean literals
     inline bool isTrue( bool value ){ return value; }
+    inline bool alwaysTrue() { return true; }
+    inline bool alwaysFalse() { return false; }
 
     void throwLogicError( std::string const& message, SourceLineInfo const& locationInfo );