Add ofstream support within the language

On the way rewrite OStream handling: << and >> are now treated as standard binary operators.

This change required the introduction of "global" variable created by module loading since now: cout, cerr and clog are no more keywords but variables of type ostream.

enabled an automatic merge when the pipeline for d30405f1 succeeds

assigned to @delpino

mentioned in commit 8d570db0

merged