C++: ESP Event wrapper classes

* Provide easy interface to esp_event in C++
* Extended functionality linke synchronous
  waiting for events

* Closes IDF-1048
* Closes IDF-232

examples/cxx/experimental/experimental_cpp_component/esp_exception.cpp

@@ -20,6 +20,10 @@ namespace idf {
 
 ESPException::ESPException(esp_err_t error) : error(error) { }
 
+const char *ESPException::what() const noexcept {
+    return esp_err_to_name(error);
+}
+
 } // namespace idf
 
 #endif // __cpp_exceptions