restructure and add ipi texs

ws2019/ipi/uebungen/cpp_headers/ggT.cc

@@ -0,0 +1,13 @@
+#include "fcpp.hh"
+
+int ggT (int a, int b)
+{
+  return cond( b==0 , a , ggT(b,a%b) );
+}
+
+
+int main (int argc, char** argv)
+{
+  return print(ggT(readarg_int(argc,argv,1),
+		   readarg_int(argc,argv,2)));
+}