Properly implement fluent interface in all writers.

Signed-off-by: Benoît Burnichon <bburnichon@gmail.com>
Fixup test detected by scrutinizer.

Signed-off-by: Benoît Burnichon <bburnichon@gmail.com>
Merge branch 'ticket_87_writer_fluent_interface' into ticket_86_stream_writer
Change CsvWriter to extends AbstractStreamWriter

Signed-off-by: Benoît Burnichon <bburnichon@gmail.com>