Add packaging

Adds Python packaging for the `xkcdpass` module. This induces some structural and some code changes. Most notably, most of the files in the repo are moved into `xkcdpass/` so that `setup.py` has a structured way of finding everything.

Things of note:

* I've added the static wordlists into the module. This has two concerns: 
    1. Are you allowed to distribute it? I can't find any solid licensing information on the originating page, but I haven't really looked a lot.
    2. Since the main script only accepts paths, it will need code change to give feasible user access to them. Before it was packaged, the wordlists lived next to the file, so just saying `-w 2of12.txt` was fairly easy. Now, the user kinda has to say `-w /usr/lib/$PYTHON/site-packages/.../2of12.txt` to be able to use these files. Making the `-w` argument accept (and suggest in `--help`) filenames from `xkcdpass/static/*.txt` is probably a good idea that would increase the general user experience. I'd love to help fix that.
* The tests are failing, but they were also failing for the current master, so I don't really take responsibility for that right now. I'd love to help with that too if needed.
* I also added a industrial-grade gitignore (the one GitHub uses as init for Python projects) and also sneaked in cracklib into default wordlists so that Linux hax0rs can get a sane default wordlist too.

This was fun! :lollipop: 

Closes #12.