Add An Abstract StreamWriter

For one of my projects, I already created a Class handling streams instead of SplObjectInfo

refs #86

Also add A utility test class StreamWriterTest for easier test stream
creation.

Signed-off-by: Benoît Burnichon <bburnichon@gmail.com>
Not really. It remained from the old CsvWriter implementation. It is not currently used.

I think it is a good idea to keep it as a basis for all stream writers. It could be an issue to write files for Windows from a Unix server.