Add tests for cpp_macro_definition parsing

include/cppast/cpp_preprocessor.hpp

@@ -16,6 +16,8 @@ namespace cppast
     class cpp_macro_definition final : public cpp_entity
     {
     public:
+        static cpp_entity_kind kind() noexcept;
+
         /// \returns A newly built macro definition.
         /// \notes It is not meant to be registered in the [cppast::cpp_entity_index](),
         /// as no other [cppast::cpp_entity]() can refer to it.