Testing and Travis-CI

I added infrastructure for testing. To run the tests:
```
python2.7 setup.py test   # other python versions ok too
```

Also, if you register with [travis-ci](http://www.travis-ci.org/), they will automatically test pyandoc against all our supported versions of Python whenever you push to GitHub.

You will need to do a `s/chaimleib/ovgu-ttz/g` on README.rst so that the README shows your test status instead of mine.

Other changes:
- Support for Python 2.6 - 2.7
- Support for Python 3.2 - 3.4
- Some README updates
- Sorted some sets in core.py