Minor improvements

* `charade` used instead of `chardet` for Python 2.6 - 3.3 compatibility
* Trove classifiers explicitly list Python 2.6, 2.7, 3.2 and 3.3 as compatible
* `tox.ini` introduced to enable testing the versions specified above with one command
* `six` explicitly listed as a requirement in `setup.py`
* README.rst is reused on the PyPI project page