include schemas.json in pypi distribution

Right now, `ordrin/schemas.json` is not being included in the pypi distribution of this package. The distribution can be found here: https://pypi.python.org/packages/source/o/ordrin/ordrin-1.0.4.tar.gz#md5=40bc70cb5162d77e15c30e6263a80ef9.

This creates a MANIFEST.in file which specifies that `schemas.json` should be included in this package's distribution. It can be tested by running `python setup.py sdist` from the root of this repository. A `dist` directory will be created that includes a zipped version of this distribution. The distribution will now include `ordrin/schema.json`.