Streaming zlib compression for the joblib.dump method.

This is a fix for #66 and #51 to avoid copying the data at pickling / compression / dump time.

To decompress I have also a nocopy implementation here:
https://github.com/ogrisel/joblib/commit/569dca33f7ab5409fba288b6e02e9e4cd090d228

However it does not work as numpy's `array.__setstate__` does not accept mutable `bytearray` instances as an alternative to immutable Python 2's `str` or Python 3's `bytes`.

I will work on a patch next week for numpy and then open a new PR that enable the nocopy mode for decompression in joblib when possible if the numpy fix is accepted upstream.