packaging with a setup.py and proper package hierarchy

it's now a python package!

to develop inside a virtualenv:
(env)$ pip install -e .

to run the tests:
(env)$ python -m unittest discover

Withouth the `:code:` bits here, these don't show up as highlighted on github.  They also don't have any quotes.

Also, I guess this was confusingly written. (I wrote it initially.)  Only `harstorage_url` is required to run the uploader, but if `har_dir` is set, it will know to look there instead of the default location.