Adding setup.py so it is installable via pip, etc


`pip install git+http://github.com/GoogleCloudPlatform/endpoints-proto-datastore.git#egg=endpoints-proto-datastore`
Got it. Thanks. Doing a [search][1] on GitHub for `setup.py` files I don't see it used much. However, your reference seems to have been written by Kenneth Reitz and he is quite good.

[1]: https://github.com/search?q=setuptools+path%3Asetup.py&type=Code&ref=searchresults