Adding OutputFormatter base class

The example scenario here is a user writing a custom formatter and is writing to the response stream...he could be having a 'using' statement around the response stream in which case it would be closed...if we implement buffering(for the sake of finding errors during serialization) at the host level in future, then the above 'using' statement would close the passed in buffered stream...so in the end we would not have a source buffer stream (as it was closed) to copy to the original response stream...