Add support for Python 3

[asgeroverby]

Minimal support for Python 3.

All tests pass with:

Robot Framework 3.0 (Python 2.7.5 on win32)
Robot Framework 3.0 (Python 3.4.3 on win32)

Note: I think the notice on Python 3 in QuickStart.rst should be updated if this pull request is accepted.

[pekkaklarck]

Is list really needed here?

[pekkaklarck]

Good idea! Please look at the notes I added, tough. It would probably be a good idea to add from __future__ import print_function to files using print too.

It's a good idea also to mention in that the guide supports Python 3. Should it be mentioned both in README.rst and in QuickStartGuide.rst? Could you add such notes too?

[asgeroverby]

Your suggestions have been implemented. Notes on Python 3 have been added / updated too.

[pekkaklarck]

Great! In a bigger project (e.g. Robot Framework) I would still ask you to squash commits, but I don't think that's really needed here. I also noticed on small typo but can easily fix it myself.

[pekkaklarck]

Thanks again for the PR. Decided to create a new release with it: https://github.com/robotframework/QuickStartGuide/releases/tag/1.1