Python 3 compatibility

[frenzymadness]

Hello.

I am trying o make this tool Python 3 compatible while keeping backward compatibility with Python 2.7. I've tested my work with three scenarios and one testing Word document. I am not a user of this tool so I just compared the output for Python 2 and 3 and it seems to be okay.

Tested commands:

officeparser.py --create-manifest --extract-streams test/test.doc
officeparser.py --dump-stream-by-name=WordDocument test/test.doc
officeparser.py --print-streams test/test.doc

If you find something missing, please provide a reproducer (shell command) so I can use it to test my work and backward compatibility.

Fixes: #18