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/include/esp_exception.hpp

@@ -22,13 +22,33 @@
 namespace idf {
 
 /**
- * General exception class for exceptions on the ESP chips.
+ * @brief
+ * General exception class for all C++ exceptions in IDF.
+ *
  * All throwing code in IDF should use either this exception directly or a sub-classes.
+ * An error from the underlying IDF function is mandatory. The idea is to wrap the orignal IDF error code to keep
+ * the error scheme partially compatible. If an exception occurs in a higher level C++ code not directly wrapping
+ * IDF functions, an appropriate error code reflecting the cause must be chosen or newly created.
  */
-struct ESPException : public std::exception {
+class ESPException : public std::exception {
+public:
+    /**
+     * @param error Error from underlying IDF functions.
+     */
     ESPException(esp_err_t error);
 
-    esp_err_t error;
+    virtual ~ESPException() { }
+
+    /**
+     * @return A textual representation of the contained error. This method only wraps \c esp_err_to_name.
+     */
+    virtual const char *what() const noexcept;
+
+    /**
+     * Error from underlying IDF functions. If an exception occurs in a higher level C++ code not directly wrapping
+     * IDF functions, an appropriate error code reflecting the cause must be chosen or newly created.
+     */
+    const esp_err_t error;
 };
 
 /**