Fixed relative imports.  Added requirements and entry point for console app to setup.py.

This fixes all the imports so you can run "python setup.py develop" (or "python setup.py install") and then run tests/test_etl.py. I also folded requirements.txt into setup.py and added the entry point "bzetl" which runs bz_etl.py:cli() (which is the former contents of the if __name__ == "__main__": clause). So you can run "bzetl" on the command line after installing to run the console app.