C++: Moved all C++ examples to own folder

* 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

examples/cxx/exceptions/main/exception_example_main.cpp

@@ -0,0 +1,56 @@
+/* C++ exception handling example
+
+   This example code is in the Public Domain (or CC0 licensed, at your option.)
+
+   Unless required by applicable law or agreed to in writing, this
+   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+   CONDITIONS OF ANY KIND, either express or implied.
+*/
+
+#include <iostream>
+
+using std::cout;
+using std::endl;
+using std::runtime_error;
+
+/* A simple class which may throw an exception from constructor */
+class Throwing
+{
+public:
+    Throwing(int arg)
+    : m_arg(arg)
+    {
+        cout << "In constructor, arg=" << arg << endl;
+        if (arg == 0) {
+            throw runtime_error("Exception in constructor");
+        }
+    }
+
+    ~Throwing()
+    {
+        cout << "In destructor, m_arg=" << m_arg << endl;
+    }
+
+protected:
+    int m_arg;
+};
+
+/* Inside .cpp file, app_main function must be declared with C linkage */
+extern "C" void app_main(void)
+{
+    cout << "app_main starting" << endl;
+
+    try {
+        /* This will succeed */
+        Throwing obj1(42);
+
+        /* This will throw an exception */
+        Throwing obj2(0);
+
+        cout << "This will not be printed" << endl;
+    } catch (const runtime_error &e) {
+        cout << "Exception caught: " << e.what() << endl;
+    }
+
+    cout << "app_main done" << endl;
+}