Merge StreamBase Class to Stream Class.

Since the Stream Class is the only class that inherits StreamBase Class, merge
them and make it a single class. This also renames the _stream_base.py to
_stream_exceptions.py since it only contains custom exceptions.

Change-Id: Ie0272762c629444247c99bc5b1723f3b64018d25

Modify tests to python 3 compatible

Change-Id: I97b1d2d1c834c61d35b8f9cfe5002e12cd83c715

Modify setup.py to add dependencies to the python six module.

This also modifies setup.py and __init__.py descriptions.

Change-Id: Ibf2b2778e49c7e8afddbe97e8180154718b33753