* spi cxx unit test (CATCH-based, on host) * added portmacro.h to driver mocking * added simple testing app to write/read SPI, using an MPU9250
* Provide easy interface to esp_event in C++ * Extended functionality linke synchronous waiting for events * Closes IDF-1048 * Closes IDF-232
* moved C++ examples to a new cxx folder in examples * added experimental C++ component * added ESPException class to the C++ experimental component * added test cases for ESPException and corresponding test macros