Py2+3 in a single module; setup.py; refactor; etc.

* Single module for both Python 2 and 3 (and it's working with PyPy as well)
* The module is now a script with a shebang (for that, end-of-line is only line feed now, without carriage return)
* Some documentation using docstrings
* Now with a `setup.py` (works for both `sdist` and `bdist_wheel`, already prepared for PyPI)
* Code refactored with a slightly more functional-programming based approach, making the bin generator unique for both column and character grouping and the character lookup based on data instead of code structure
* Resulting plots aren't different for Python 2 and 3 anymore (previously, the first example when calling the script wasn't behaving the same way).