include package data when installing the package

`import ordrin` is failing with the error: `IOError: [Errno 2] No such file or directory: '/Users/michaelkolodny/.virtualenvs/surpriseme/lib/python2.7/site-packages/ordrin/schemas.json'`. While `schemas.json` is being included in the PyPI distribution of the ordrin package, the file isn't installed. That's happening because the files listed in `MANIFEST.in` are not being included.

This tells setuptools to install all the files in `MANIFEST.in` when installing the ordrin package.