added package_dir argument to setup()

ordrin/schemas.json is not being included when ordrin is installed via PyPI (`pip install ordrin`). That's happening because setup() is only looking in the distribution root for .json files, rather than in /ordrin.
This tells setup() to look for .json files in the /ordrin directory.
For more details, see: http://docs.python.org/2/distutils/setupscript.html#installing-package-data; and http://docs.python.org/2/distutils/sourcedist.html#principle.