Switched to use JSON instead of CSV

It outputs JSON to stdout instead of CSV. I tweaked some of the PyQuery syntax, and I think it's better, but honestly I'm new to PyQuery too.

I also added a `requirements.txt` file, which means people can install dependencies with `pip install -r requirements.txt`. I also added a `.python-env` file, which is only useful if you use [pyenv](https://github.com/yyuu/pyenv) (which I do, but I don't know anyone else who does yet).