Add possibility to silent outputs or to redirect them

This is made in view of parallelism. One will be able to silent processors
or/and produce file output

src/utils/PastisOStream.cpp

 #include <PastisOStream.hpp>
 
+#include <sstream>
+#include <iomanip>
+
 PastisOStream pout(std::cout);
 PastisOStream perr(std::cerr);
+
+std::stringstream null_stream;
+const PastisOStream _null_stream_initializer(*[](std::stringstream& null_stream){
+                                                null_stream.setstate(std::ios::badbit);
+                                                return &null_stream;}(null_stream));

src/utils/PastisOStream.hpp

@@ -3,6 +3,9 @@
 
 #include <PastisMacros.hpp>
 #include <iostream>
+#include <sstream>
+
+extern std::stringstream null_stream;
 
 class PastisOStream
 {
@@ -37,5 +40,6 @@ class PastisOStream
 
 extern PastisOStream pout;
 extern PastisOStream perr;
+extern const PastisOStream _null_stream_initializer;
 
 #endif // PASTIS_OSTREAM_HPP