move kitchen-sink demo into a separate directory

demo/docs/cpp.cpp

@@ -1,13 +0,0 @@
-// compound assignment operators
-
-#include <iostream>
-using namespace std;
-
-int main ()
-{
-    int a, b=3; /* foobar */
-    a = b;
-    a+=2; // equivalent to a=a+2
-    cout << a;
-    return 0;
-}