TXT and CSV Functors completed and tested

Both the TxtFunctor and the CsvFunctor have been completed and
tested, and a new header file for utils has been introduced.

Signed-off-by: Raffaele Aquilone <aquiloneraf@gmail.com>
JSON functor completed and tested

Completed JSON functor and fixed some minor issue in other
functors.

Signed-off-by: Raffaele Aquilone <aquiloneraf@gmail.com>
XML functor completed and tested

Now all functors have been completed and tested

Signed-off-by: Raffaele Aquilone <aquiloneraf@gmail.com>